University  of  California  •  Berkeley 


DEPARTMENT  OF  THE  INTERIOR-U.  S,  GEOLOGICAL  SURVEY 
CHARLES   1).  WALCOTT,  JMIIKCTOU 


THE 

MINING  DISTRICTS  OF  THE  IDAHO  BASIN  AND  THE 

BOISE  RIDGE,  IDAHO 
f 

BY 

WALDKMAR    LINDG-RKTST 


WITH  A  REPORT  ON  THE  FOSSIL  PLANTS  OF  THE 
PAVETTE  FORMATION 


FRANK 


,  TCNOWLTON 


EXTRACT  FROM  THE  EKIHTEEXTII  ANNUAL  REPORT  OF  THE  SURVEY,  1896-97 
1'AIiT    III— ECONOMIC   OEOLOOY 


WASHINGTON 

GOVERNMENT   PRINTING   OFFICE 
1898 


THE  MINING  DISTRICTS  OF  THE  IDAHO  BASIN 
AND  THE  BOISE  RIDGE,  IDAHO, 

BY 

WALDEMAR    LIISTDGKREN; 

if 

WITH 

A  REPORT  ON  THE  FOSSIL  PLANTS  OF  THE  PAYETTE  FORMATION, 

B'Y 


617 


CONTENTS. 


Page. 

CHAPTER  I. — General  topography  and  geology 625 

Geographical  position 625 

Snake  River  Valley .. _  625 

Literature , 626 

Topography 628 

Geological  history 630 

Pre-Tertiary 630 

The  Payette  formation 632 

Early  Neocene  volcanic  activity 634 

Post-Payette  erosion ... 635 

Post-Payette  orographic  disturbances 635 

Late  Neocene  basalts ...  636 

Post-basaltic  erosion..   ,. 636 

Resume  of  geological  events  in  the  lower  Snake  River  Basin 637 

CHAPTER  II. — The  ore  deposits  in  general 638 

General  features 638 

Alteration  of  the  country  rock _ ._. 638 

Silicification ...   645 

Structure  of  the  veins. ... 647 

Mineral  deposits  of  post-Neocene  age .  _  _ 648 

CHAPTER  III. — The  Idaho  Basin 651 

Geographical  position ... 651 

Discovery  and  history ,-. 651 

Production . 652 

Topography.. 656 

Grades  of  the  water  courses . .' 657 

Tertiary  and  Pleistocene  formations 657 

Lower  Moore  Creek  Valley .... .  657 

Configuration  of  valley .  657 

The  basalt  flow 658 

The  present  stream  gravels .... 658 

The  gravels  below  the  basalt 658 

High  gravels .  659 

Upper  Moore  Creek  Valley. . 659 

Configuration  of  valley ...  659 

The  present  stream  gravels 660 

Bench  gravels _.   . 660 

High  gravels 662 

Lake  beds 665 

Gold  in  the  lake  beds 668 

Olivine  basalt  (dolerite) _.  - 669 

The  valley  of  Grimes  Creek 669 

Configuration 669 

619 


620  CONTENTS. 

CHAPTER  III— Continued.  Page. 
Tertiary  and  Pleistocene  formations — Continued. 
The  valley  of  Grimes  Creek — Continued. 

Present  stream  gravels.. 670 

Bench  gravels --  670 

Older  gravels 671 

Lake  beds 671 

Volcanic  rocks -  672 

The  valley  of  Granite  Creek 672 

Configuration ...-_,  672 

Present  stream  gravels 672 

Bench  gravels .-  672 

Older  gravels.. 673 

Gravel  on  the  Boise  Range 675 

Basalt _ '....  675 

Fineness  of  the  gold 676 

Water  supply... : 676 

Moore  Creek 676 

Grimes  Creek ... 677 

Granite  Creek 677 

Ground  available  for  future  work ...  677 

The  monazite  sands 677 

Relation  between  placers  and  quartz  veins 680 

CHAPTER  IV. — The  Idaho  Basin  (continued) 681 

The  pre-Tertiary  rocks ^. 681 

Granite - 681 

Dikes  associated  with  the  granite 682 

The  quartz  veins 684 

The  Idaho  City  gold  belt 684 

The  Elaine  vein 684 

The  Chickahominy  vein. 684 

The  Illinois  vein 684 

The  Populist  vein 685 

The  Cleveland  vein... 685 

The  Gambrinus  (Surprise)  vein 686 

The  Boulder  vein 686 

The  Mona  MacCarthy  vein. 687 

The  Sub-Rosa  or  Forest  King  vein 687 

The  Elkhorn  vein... 689 

The  Summit  vein 689 

The  Quartzburg-Grimes  Pass  gold  belt 689 

The  Ebenezer  vein.. .".„  690 

The  Gold  Hill  vein 691 

The  Iowa  vein 692 

The  Carroll  veins ..._.- 692 

The  Kennebec  claim 693 

Veins  at  head  of  Wolf  Creek 693 

The  veins  in  the  porphyry  dike  east  of  Wolf  Creek 693 

Claims  near  Grimes  Pass  _. 694 

Mining  districts  east  of  the  basin 695 

Fineness  of  the  quartz  gold 696 

The  geological  history  of  the  Idaho  Basin 696 

CHAPTER  V. — The  mining  districts  of  the  Boise  Ridge 699 

Neal  mining  district 699 


CONTENTS.  621 

CHAPTER  V. — The  mining  districts  of  the  Boise  Ridge— Continued.  page. 
Neal  mining  district — Continued. 

Location 699 

Topography 699 

Geology 700 

The  veins 701 

Black  Hornet  mining  district 703 

Topography 703 

Geology 704 

Mineral  deposits. 704 

Boise  mining  district 705 

Shaw  Mountain  mining  district. 707 

Mining  districts  of  Willow  Creek  and  Rock  Creek 707 

Location  and  topography 707 

Geology 708 

Granitic  rocks 708 

Dike  rocks 710 

The  Payette  formation 711 

Rhyolite. 712 

Basalt 712 

The  ore  deposits. 712 

General  character .. , 712 

Treatment  of  the  ores 714 

Detailed  description 714 

Silver  deposits .. 718 

Placers  of  the  Boise  Ridge 718 

Recent  placers : 718 

Neocene  placers 719 

APPENDIX:  The  fossil  plants  of  the  Payette  formation,  by  F.  H.  Knowlton.  721 

Systematic  enumeration  of  species 721 

Discussion  of  the  flora  and  its  bearing  on  the  age  of  the  beds 735 


ILLUSTRATIONS. 


Page. 

PLATE  LXXXVII.  General  map  of  the  lower  Snake  River  Valley,  Idaho-...  625 
LXXXVIII.  Head  of  Boise  Valley,  8  miles  southeast  of  Boise,  look- 
ing northwest,  showing  basalt  table  and  Pleistocene 

terraces 632 

LXXXIX.  Upper  canyon  of .  Brainard  Creek,  Jerusalem  Valley, 
Boise  Ridge,  showing  tilted  basalt  flows  resting  on 

granite 636 

XC.  Types  of  gold-bearing  fissure  veins GoO 

XCI.  The  Idaho  Basin,  looking  east  from  the  Jerusalem  Road 

west  of  Quartzburg _•_ 656 

XCII.  Lower  Valley  of  Moore  Creek,  3  miles  above  its  mouth, 

showing  basalt  flow  cut  through  by  the  creek 658 

XCIII.  Idaho  City  from  Gold  Hill,  looking  southwest,  showing 

tailings  and  bench  gravels 660 

XCI  V.  Working  bench  gravels  by  the  hydraulic  process  at  Idaho 

City 662 

XCV.  Gravel  bank  with  underlying  lake  bed  at  Plowman's 

claim,  East  Hill,  Idaho  City,  looking  southwest 664 

XCVI.  Geological  map  of  the  Idaho  Basin In  pocket 

XCVII.  Map  of  the  Neal  mining  district,  by  F.  D.  Howe 700 

XCVIII.  Map  of  the  Willow  Creek  and  Rock  Creek  mining  dis- 
tricts   708 

XC1X.  Fossil  leaves,  Pay ette  beds 738 

C.  Fossil  leaves,  Payette  beds 740 

CI.  Fossil  leaves,  Payette  beds 743 

GIL  Fossil  leaves,  Payette  beds 744 

FIG.  55.  Gravel  benches,  1£  miles  below  Idaho  City 681 

56.  Section  of  highest  bench,  1 J  miles  below  Idaho  City 662 

57.  Section  across  lake  beds  and  gravels  at  Idaho  City 663 

58.  Exposure  of  lake  beds  and  auriferous  gravel,  l£  miles  south  of 

Idaho  City. 665 

59.  Bench  gravel  and  lake  beds  at  mouth  of  Granite  Creek,  2  miles 

west  of  Idaho  City 666 

60.  Bank  of  bench  gravels,  one-fourth  mile  north  of  Pioneerville, 

level  of  Grimes  Creek 671 

61.  Bank  at  the  Ranch  Company's  claim,  Placerville 674 

62.  Diagram  of  fault  in  the  Cleveland  vein 686 

63.  Section  of  Mountain  Chief  vein,  east  end  of  claim 690 

64.  Breast  of  drift,  Carroll  vein 693 

65.  Cross  section  of  vein  in  the  Neal  mining  district 701 

623 





THE  MINING  DISTRICTS  OF  THE  IDAHO  BASIN  AND  THE 
BOISE  RIDGE,  IDAHO,1 


By  WALDEMAR  LINDGREN. 


CHAPTER  I. 
GENERAL  TOPOGRAPHY  AND  GEOLOGY. 

GEOGRAPHICAL   POSITION. 

The  region  shown  in  PI.  LXXXVII  includes  a  portion  of  the  lower 
Snake  River  Valley  and  the  mountains  adjacent  on  the  northern  side. 
The  total  area  is  about  13,500  square  miles.  It  embraces,  besides  a 
part  of  the  Snake  River,  almost  the  whole  drainage  of  the  Payette, 
Boise,  and  Wood  rivers,  and,  in  the  northeastern  corner,  a  part  of 
that  of  the  Salmon  River.  The  irregular  mountain  complex  within 
the  drainage  of  the  Boise  and  the  Payette  rivers  is  designated  the 
"Boise  Mountains;  "  along  the  parting  between  these  rivers  and  the 
Salmon  River  drainage  rise  a  series  of  sharp  peaks,  usually  referred 
to  as  the  "  Sawtooth  Range."  The  "  Boise  Ridge  "  extends  from  the 
Boise  to  beyond  the  Payette  just  west  of  longitude  116°,  and  attains 
elevations  of  over  7,000  feet.  The  Idaho  Basin  is  an  interniontane 
valley  in  the  Boise  Mountains  south  of  latitude  44°  and  east  of  longi- 
tude 116°. 

The  map  shows  the  positions  and  names  of  the  quadrangles  repre- 
sented by  the  topographic  sheets  issued  by  the  United  States  Geolog- 
ical Survey.  It  also  shows,  in  a  somewhat  generalized  way,  the  geology 
of  a  part  of  the  area. 

SNAKE  RIVER  VALLEY. 

The  discussion  of  the  geology  of  this  district  necessitates  a  short 
reference  to  the  large  Snake  River  Valley  and  an  abstract  of  previous 
work  relating  to  its  remarkable  geological  features.  The  Snake  River 
Valley  stretches  across  the  whole  width  of  southern  Idaho  in  a  broad 
curve  opening  toward  the  north  and  having  a  radius  of  160  miles.  The 
length  of  this  valley  from  the  base  of  the  Tetons  to  Weiser,  where  the 
river  enters  into  a  narrow  canyon,  is  over  400  miles,  while  its  width 

1  The  field  work  upon  which  this  report  is  based  was  done  during  the  summer  and  fall  of  1896 
by  the  author,  assisted  by  Dr.  E.  C.  E.  Lord. 

18  GEOL,  PT  3 40  625 


626  IDAHO    MINING    DISTRICTS. 

ranges  from  50  to  125  miles,  its  total  area  being  about  34,000  square 
miles.  The  grade  of  the  river  is  moderate.  At  Blackfoot  the  eleva- 
tion is  4,505  feet,  and  350  miles  lower  down,  at  Weiser,  it  is  2,125  feet, 
giving  an  average  grade  of  less  than  7  feet  per  mile  between  these 
places.  On  both  sides  of  this. valley  rise  higher  ranges,  chiefly  of 
granite  in  the  lower  valley,  of  granite  and  Paleozoic  and  Mesozoic 
rocks  in  the  upper  valley.  The  lower  slopes  of  these  ranges  are  often 
flanked  by  Tertiary  lake  deposits.  The  larger  part  of  the  valley  is 
occupied  by  vast  flows  of  basalt,  frequently  resting  upon  and  covered 
by  fluviatile  and  lacustrine  accumulations  contemporaneous  with  the 
flows.  The  basalt  of  the  Snake  River  Valley  bears  evidence  of  being 
throughout  of  the  same  age  approximately,  though  consisting  of  a  great 
number  of  individual  flows,  and  has  generally  been  regarded  as  Plio- 
cene. The  eruptions  did  not  originate  from  large  volcanoes.  Ashes 
and  other  fragmentary  rocks  are  generally  absent,  and  the  basalt  evi- 
dently flowed  out  quietly  and  without  explosions  from  numerous  local 
vents  along  the  margin  of  the  valley  or  within  the  valley  itself.  This 
volcanic  action  is  usually  referred  to  as  fissure  eruption,  but  it  must  not 
be  inferred  that  these  fissures  were  long  or  large.  It  appears  rather  as 
if  the  vents  had  the  character  of  rounded  local  orifices,  hardly  exten- 
sive enough  to  be  classed  as  fissures.  The  basalts  often  flowed  down 
from  the  foothills  of  older  rocks,  closely  following  the  present  can- 
yons, though  the  streams  have  since  then  generally  succeeded  in 
wearing  through  the  filling  in  their  bottoms.  Thus  it  is,  for  instance, 
along  the  Boise  River. 

It  will  be  shown  that  the  Snake  River  Tertiaries  consist  of  a  thick 
series  of  early  Neocene  (Miocene)  lake  beds,  with  which  are  associated 
vast  masses  of  eruptives  distinct  from  the  Snake"  River  basalts  proper, 
and  another  series  of  deposits  of  late  Neocene  age  (Pliocene),  consist- 
ing of  the  Snake  River  basalts  and  associated  sedimentary  rocks. 
These  two  terranes  represent  successive  stages  of  the  Neocene  lake 
and  are  often  difficult  to  separate. 

LITERATURE. 

The  upper  Snake  River  Basin  has  been  described  by  Messrs. 
Hayden,1  Bradley,2  Peale,3  and  St.  John,4  in  the  reports  of  the  United 
States  Geological  and  Geographical  Survey  of  the  Territories. 
Hayden  describes  the  basalt  flow  along  the  present  line  of  the  Utah 
and  Northern  Railroad,  mentioning  that  there  were  several  flows  of 
basalt,  or  at  least  two,  separated  by  somewhat  tilted  Pliocene  depos- 
its of  slight  depth.  St.  John  and  Peale  describe  the  basalt  flows  east 
of  this,  near  the  headwaters  of  the  Snake  River.  Peale  states  that  a 
number  of  extinct  craters  exist,  that  there  were  several  flows  of 

1  U.  S.  Geol.  and  Geog.  Surv.  Terr.,  Kept.  1871,  pp.  25-30. 

2  Ibid.,  Kept.  1872,  p.  190. 

3  Ibid.,  Rept.  1877,  p.  543. 
4Ibid.,Eept.  1877,  p.  323. 


LINDOREN.]  SNAKE    RIVER   VALLEY.  627 

basalt,  and  that  the  basalts  are  generally  horizontal  in  position  and 
fill  the  valleys  and  the  more  depressed  portions  of  the  basins.  There 
appear  to  have  been  two  periods  of  basaltic  flows,  one  at  the  close  of 
the  Pliocene,  the  other  at  the  beginning  of  the  Pleistocene.  The 
Pleistocene  age  is  inferred  from  exposures  at  Marsh  Valley,  near 
Red  Rock  Pass,  where  Pleistocene  beds  were  somewhat  eroded  before 
the  basaltic  flow. 

According  to  Gilbert,  however,  this  Pleistocene  is  older  than  the 
highest  stage  of  Lake  Bonneville,  during  which  the  lake  found  an 
outlet  at  Red  Rock  Pass.  The  river  draining  the  lake  at  this  time 
appears  to  have  flowed  over  the  surface  of  the  basalt. 

According  to  Hague,1  the  latest  eruptions  in  the  Yellowstone 
National  Park  are  of  basalts,  which  stretch  far  into  Idaho  in  somber, 
monotonous  beds.  These  basalts  are  pre-Glacial,  and  their  eruption 
is  referred  to  the  Pliocene. 

About  1869  Mr.  Clarence  King  visited  the  lower  part  of  the  Snake 
River  basin  and  collected  a  number  of  fossils  from  beds  beneath  the 
basalt  at  Castle  and  Sinker  creeks,  tributaries  from  the  south,  joining 
the  river  about  due  south  of  Boise.  The  fossils  have  been  described 
in  detail,  while  no  description  of  the  localities  was  ever  published,  a 
fact  which  has  led  to  some  confusion.  A  few  notes  regarding  this 
occurrence  are  contained  in  King's  Systematic  Geology2  and  may  be 
quoted : 

In  the  basin  of  Snake  River  .  .  .  there  were  basaltic  eruptions  in  the  middle 
of  the  Pliocene  period  which  overflowed  the  earlier  lacustrine  beds  of  the  period, 
and  in  turn  were  themselves  overlaid  ...  by  the  main,  later  Pliocene  series. 
.  .  .  Sections  obtained  along  the  plains  between  the  Owyhee  Mountains  and  Snake 
River  show  that  a  considerable  portion  of  the  beds  of  the  valley,  which  consist 
chiefly  of  white  sands  and  marls  carrying  numerous  well-defined  Pliocene  forms, 
were  overlaid  by  large  accumulations  of  basaltic  flow,  and  that  subsequently  a 
second  period  of  lacustrine  deposition  took  place,  likewise  characterized  by  Plio- 
cene forms,  the  latter  representing  a  more  advanced  stage  of  development  and 
more  recent  type  than  those  beneath  the  basalt. 

King  further  states  that  near  Shoshone  Falls  the  basalt  rests  on 
the  eroded  surface  of  a  trachytic  soft  rock  which  he  considers  of  pre- 
Miocene  age.3  From  the  collections  of  King  and  the  later  collections 
of  Wortman,  Cope  has  described  an  extensive  fauna  of  fresh-water 
fishes,  and  proposed  for  the  sediments  in  which  these  are  contained 
the  name  Idaho  formation.* 

The  locations  given  are  very  vague,  as  "Catherine  Creek,"  " Castle 
Creek,"  or  "Southern  Idaho,"  and  no  description  of  the  beds  is 
vouchsafed.  The  fauna  consists  of  22  species,  all  differing  from 
existing  species  so  far  as  known.  Professor  Cope  thinks  that  the 

1  Am.  Jour.  Sci.,  4th  series,  June,  1896,  Vol.1,  p.  455. 
»U.  S.  Geol.  Expl.  Fortieth  Par.,  Vol.  1, 1878,  pp.  418,  440. 
a  Ibid.,  p.  593. 
t    «Proc.  Phila.  Acad.  Sci.,  1883,  pp.  153-166. 


628  IDAHO    MINING    DISTRICTS. 

evidence  clearly  indicates  a  Pliocene  age.  From  the  same  beds 
were  obtained  three  species  of  crawfishes  specifically  distinct  from 
all  others  described  from  the  West.  Mammalian  remains  were  also 
collected  by  King  from  similar  beds  on  Sinker  Creek,  which  were 
determined  by  Leidy  to  be  Mastodon  mirificus  and  Equus  excelsus, 
both  of  which  belong  to  the  Niobrara  Pliocene  fauna.  A  few  mol- 
lusks  have  also  been  found  in  the  same  deposits  on  Sinker  Creek. 
Thus  Meek1  described  Sphaerium  (?)  idahoense  Meek  from  Castle 
Creek,  collected  by  King.  Gabb2  described  two  species,  Melania 
taylori  Gabb  and  LHhasia  antiqua  from  a  "Deposit  on  Snake  River 
on  the  road  from  Boise  to  the  Owyhee  mining  country;"  thus  probably 
from  Walters  Ferry.  The  same  forms  have  been  found,  according 
to  Mr.  George  II.  Eldridge,  at  Glenns  Ferry,  120  miles  above  Walk- 
ers Ferry.  Dr.  White  describes  the  same  two  species  and  another, 
Latia  dallii,  from  a  point  50  miles  below  Salmon  Falls,  Snake  River, 
which  probably  refers  to  Glenns  Ferry,  and  states  that  these  forms 
differ  considerably  from  any  known  fresh-water  fauna  of  America 
either  fossil  or  living.3  Both  Meek  and  White  are  in  favor  of  corre- 
lating these  Tertiary  beds  with  King's  Truckee  Miocene.  To  this  the 
utterances  of  King  are  directly  opposed,  and  it  is,  indeed,  from 
stratigraphic  grounds,  improbable  that  these  beds  are  of  Miocene 
age.  Near  Glenns  Ferry  beds  of  sand  and  clay  occur  intercalated 
between  the  basalt  flows,  and  it  is  probable  that  the  fossils  came  from 
this  locality  and  that  all  of  them  were  collected  in  beds  very  closely 
associated  with  the  late  basaltic  eruptions,  from  which  it  would 
follow  that  they  should  be  placed  in  the  latest  Pliocene. 

Prof.  O.  C.  Marsh  states  (oral  communication,  January,  1897)  that 
a  large  amount  of  Pliocene  mammalian  remains  was  found  in  a  bluff 
about  100  feet  above  the  Snake  River,  some  distance  below  Weiser,  at 
the  old  crossing  of  the  stage  road  to  Oregon,  on  the  Oregon  side  of  the 
river. 

None  of  these  localities  were  visited  during  the  field  season  of  1896 
on  account  of  pressing  economical  and  areal  work  in  other  sections ; 
but  from  the  area  studied  it  was  possible  to  read  in  its  chief  features 
the  later  geologic  history  of  the  lower  part  of  the  Snake  River  basin. 
The  correlation  of  these  results  with  the  older  work  remains  for  the 
future. 

TOPOGRAPHY. 

The  chief  topographic  features  of  the  region,  of  which  the  geology 
is  shown  on  PI.  LXXX VII,  are  as  follows : 

Broad  flat  mesas  of  basalt  and  Pliocene  lake  beds  spread  on  both 
sides  of  Snake  River,  though  chiefly  on  the  northern  side.  Through 
these  mesas  the  river  has  cut  an  abrupt  canyon,  bordered  by  basaltic 

1  Proc.  Phila.  Acad.  Nat.  Sci.  1870,  p.  57. 

3  Paleontology  of  Gal.,  Vol.  II,  p.  13. 

'  Proc.  U.  S.  Nat.  Mus.  1882,  Vol.  V,  p.  99. 


UNI-"!";*.-!  TOPOGRAPHY    OF    THE    REGION.  629 

cliffs,  to  a  depth  of  from  200  to  700  feet.  The  low  mesas,  surmounted 
by  several  buckles  or  domes  of  basalt  a  few  hundred  feet  high,  rise 
gradually  toward  the  edge  of  the  mountain.  Near  the  mouth  of  the 
Boise  River  the  basalt  mesas  cease,  and  from  here  down  to  Weiser, 
where  the  great  Snake  River  canyon  begins,  several  large  tributaries 
enter,  such  as  the  Payette  and  the  Owyhee,  and,  at  elevations  of  from 
2,200  to  2,700  feet,  level  bottom  lands  and  broad  low  terraces  flank 
the  water  courses. 

Between  the  mouth  of  the  Boise  and  Weiser  flat-topped  hills  of  soft 
sandstones  rise  on  both  sides  of  the  Snake  River  to  a  height  of  600  to 
800  feet.  Similar  complexes  of  higli  sandy  mesas  rise  between  the 
lower  courses  of  the  Boise  and  the  Payette  and  north  of  the  Payette. 
The  mountains  of  older  rocks  surrounding  the  tectonic  trough  of  the 
Snake  River  Valley  rise  gradually,  on  the  north  side  of  the  river, 
beyond  the  sloping  mesas  of  Tertiary  rocks,  their  margin  having  a 
northwesterly  direction  in  this  vicinity.  The  transition  between 
mountains  and  mesa  is  abrupt  only  at  the  Boise  River,  near  Boise, 
and  the  abruptness  is  here  due  to  the  extensive  erosion  of  the  Payette 
sandstones  by  the  river. 

The  mountain  region  extending  up  to  the  Sawtooth  Range,  dividing 
with  a  north-northwesterly  trend  the  waters  of  the  Boise  and  the  south- 
ern branches  of  the  Payette  from  those  of  the  Salmon,  has  an  average 
width  of  5,5  miles  and  culminates  in  summits  with  an  elevation  of  from 
10,000  to  11,000  feet.  This  mountain  complex,  which  is  made  up  chiefly 
of  granitic  rocks,  does  not  form  a  well-defined  range,  but  rather  a 
broad  uplift  dissected  deeply  and  in  the  most  intricate  manner  by  the 
forks  of  the  Boise  and  the  Payette.  The  summits  of  the  narrow  ridges 
generally  form  gently  sloping  lines.  If  a  surface  were  constructed 
containing  all  these  lines  it  would  be  of  undulating,  curved  character, 
sloping  gently  from  elevations  of  9,000  down  to  4,000  feet.  From  the 
southwestern  edge  a  steeper  slope  carries  the  granitic  rocks  below  the 
surface  of  the  Tertiary  rocks  of  the  Snake  River  Valley.  The  can- 
yons of  the  Boise  and  the  Payette  have  cut  down  in  the  uplift  to  a 
maximum  depth  of  3,000  feet,  and  are  joined  by  deep  lateral  canyons, 
dividing  the  whole  region  into  a  maze  of  narrow  aretes.  The  grade  of 
the  main  rivers  is  relatively  low,  from  10  feet  up  to  50  feet  per  mile, 
and  only  well  up  toward  the  head  waters  are  grades  of  100  feet  per 
mile  attained.  The  grades  of  the  lateral  canyons  are  also  often  rela- 
tively slight  in  their  lower  course,  but  extremely  steep  cirques  rise 
near  their  head  waters.  The  Idaho  Basin  quadrangle  offers  excel- 
lent illustrations  of  these  relations,  which  are  the  result  partly  of  a 
considerable  antiquity  of  the  drainage,  partly  of  the  crumbling  char- 
acter of  the  granite.  At  the  main  divide  (Bear  Valley  quadrangle) 
the  broad  valleys  and  gentler  slopes  of  the  Salmon  River  drain- 
age contrast  strongly  with  the  deeply  incised  canyons  of  the  Boise 
and  Payette.  The  latter  streams  are  continually  capturing  territory 


630  IDAHO    MINING    DISTRICTS. 

belonging  to  the  former,  and  the  divide  is  in  process  of  migration  north- 
eastward. The  whole  region  may  be  regarded  as  an  uplifted  sloping 
plateau  deeply  dissected  by  a  drainage  system,  whose  origin  evidently 
antedates  the  Miocene  period.  Smaller  individual  ranges  occur  in  a 
few  places,  as  in  the  Boise  Ridge,  rising  to  elevations  of  7,500  feet 
and  extending  due  north,  dividing  the  Idaho  Basin  from  the  waters 
of  the  Payette.  This  range  also  crosses  the  South  Fork  of  the  Payette 
and  continues  for  some  distance  north  of  it.  Within  this  mass  of 
mountains  several  depressions  or  basins  with  gentler  slopes  also  exist, 
such  as  the  Idaho  Basin,  the  Dead  wood  Basin,  and  Smiths  Prairie, 
which  have  been  created  or  emphasized  by  more  recent  orographic 
movements.  Evidences  of  glacial  topography  occur  only  near  the 
Sawtooth  and  Trinity  mountains.1  The  lower  area  here  specially 
described  has  never  been  covered  by  ice. 

GEOLOGICAL  HISTORY. 

The  vicinity  of  Boise  River,  where  it  debouches  from  the  mountains, 
proved  to  be  an  exceptionally  fortunate  location  for  the  study  of  the 
geological  history  of  this  part  of  the  Snake  River  drainage,  for  the 
record  left  by  the  river  of  successive  geological  events  back  to  a  cer- 
tain date  is  remarkably  clear  and  easy  to  read. 

PRE-TERTIARY. 

The  oldest  rock  exposed  is  the  granite  of  the  Boise  Mountains.  This 
forms  an  extremely  large  area,  embracing,  so  far  as  known,  the  whole 
of  the  upper  drainage  of  the  Boise  and  Payette  rivers  and  extending 
northeastward  beyond  the  Sawtooth  Mountains  and  eastward  as  far 
as  Wood  River,  where  it  is  adjoined  by  sedimentary  rocks  of  probr 
ably  Carboniferous  age.2  This  rock  is  largely  a  typical,  coarse  gran- 
ite of  gray  or  yellowish-gray  color,  consisting  of  orthoclase  in  often 
large  crystals,  plagioclase,  quartz,  biotite,  and  sometimes  muscovite. 
Pegmatite  dikes  are  common  in  many  places.  Locally  the  granite 
contains  hornblende,  and  is  by  gradual  transition  connected  with 
intermediate  rocks  standing  between  granite  and  diorite,  and  also, 
though  more  rarely,  with  diorites.  Narrow  dikes  of  light-colored 
granite-porphyry  and  dark  lamprophyric  dike  rocks,  chiefly  minettes, 
are  abundant  and  present  a  great  variety  of  structural  types.  A  belt 
characterized  by  dikes  of  coarse  quartz-diorite,  porphyrites,  and  occa- 
sional occurrences  of  gabbro  and  diabase  extends,  with  one  short  inter- 
ruption, from  the  vicinity  of  Wilson  Peak,  east  of  the  Idaho  Basin,  by 
Quartzburg,  to  the  Willow  Creek  mining  district.  All  of  these  dikes 
are  probably  connected  with  the  granite  eruption — that  is,  they  were 
intruded  shortly  after  the  consolidation  of  the  granite.  Within  the 
area  described  the  granite  is  remarkably  unaltered  and  massive,  no 

1  George  H.  Eldridge,  Sixteenth  Ann.  Kept.  U.  S.  Geol.  Survey,  Part  II,  1895,  p.  :*>:!. 

2  George  H.  Eldridge,  loc.  cit. 


LINDOKEN.]  PRE-TERTIARY    ROCKS.  631 

bodies  of  schist  appearing  in  connection  with  it.  It  weathers  easily 
and  crumbles  to  a  coarse  sand  which  largely  covers  the  hillsides. 
Only  in  the  higher  mountains  and  along  the  bottom  of  the  canyons 
are  satisfactory  exposures  found.  The  age  of  this  granite,  which  is 
clearly  of  igneous  and  intrusive  origin,  is  an  open  question.  Messrs. 
Becker1  and  Eldridge2  assign  to  it  provisionally  an  Archean  age,  but 
a  thorough  study  of  its  contact  with  surrounding  formations  is  neces- 
sary before  its  age  can  be  determined.  The  granite  is  in  many  places 
traversed  by  shear  planes,  giving  it  a  jointed  or  sheeted  structure, 
and  often  these  planes  coincide  with  the  direction  of  the  fissures  on 
which  mineral  veins  occur.  It  is  probable  that  these  two  features 
are  of  the  same  and  contemporaneous  origin.  Nearly  all  of  the  pri- 
mary mineral  deposits  are  contained  in  the  granite  or  allied  porphy- 
ries. By  far  most  of  them  have  a  direction  ranging  from  E.-W.  to 
ENE.-WSW.,  and  dip  to  the  south  at  angles  from  40°  to  85°  from  the 
horizontal.  While  it  is  probable  that  all  of  them  belong  to  the  same 
period  of  formation,  there  are  few  definite  clews  to  their  age.  It  is 
likely,  however,  that  they  are  post-Carboniferous,  and  it  is  certain 
that  they  antedate  the  Miocene  lake  deposits.  A  Cretaceous  or  early 
Tertiary  age  may  provisionally  be  assigned  to  them.  The  mode  of 
their  occurrence  indicates  beyond  doubt  an  origin  by  deposition  from 
mineral  waters,  probably  ascending  hot  springs:  A  slight  recurrence 
of  the  vein-forming  activity  occurred  after  the  Neocene  period. 

Before  the  beginning  of  the  Neocene  the  chief  features  of  the  topog- 
raphy were  outlined — the  broad  uplift  of  the  Boise  Mountains  and  the 
depression  of  Snake  River  Valley.  The  latter  is  not  unlikely  a  sunken 
area  separated  by  old  fault  lines  from  the  mountains  to  the  north. 
At  that  time  the  basalt  flows  and  the  lake  beds  did  not  exist,  but  the 
drainage  of  the  Boise,  and  probably  also  of  the  upper  Payette  River, 
was  outlined  in  practically  its  present  form.  The  granitic  range  pre- 
sented a  bold  scarp  facing  the  valley,  and  the  canyon  of  the  Boise 
R^ver  was,  at  its  debouchure  from  the  mountains,  cut  to  practically 
the  same  depth  which  it  has  at  present.  It  had  not,  of  course,  cut 
back  so  far  toward  the  Sawtooth  Range  as  at  present,  and  many 
features  of  the  drainage,  notably  in  the  Idaho  Basin,  were  different 
from  those  existing  now.  As  substantiating  this  it  will  be  shown  that 
the  Miocene  lake  beds  fill  the  old  canyon  at  the  gate  of  the  moun- 
tains, 10  miles  southeast  of  Boise,  and  that  in  front  of  it  lie  enormous 
masses  of  coarse  Neocene  gravel  and  conglomerate.  Thus  the  time 
immediately  preceding  that  from  which  the  first  records  date  was  one, 
first,  of  uplift  and  subsidence,  during  which  the  rough  features  were 
blocked  out,  and  second,  one  of  long-continued  erosion,  during  which 
the  Boise  Mountains  were  dissected  and  the  debris  from  the  excavated 
canyons  deposited  in  the  basin  of  the  Snake  River  Valley,  where  it  is 

1  Tenth  Census,  Precious  Metals,  p.  54. 

2  Loc.  cit. 


632  IDAHO    MINING    DISTK1CT8. 

now  deeply  covered  below  later  formations.  If  we  should  venture 
tentatively  to  go  back  one  step  further,  it  might  be  suggested  that 
the  uplifted  surface  of  the  Boise  Mountains  is  probably  the  result  of 
a  far  older  erosion,  of  early  Tertiary  or  Cretaceous  age,  which  planed 
down  a  more  ancient  range  to  gentler  outlines,  or  to  a  peneplain. 

THE   PAYETTE   FORMATION. 

During  the  earlier  part  of  the  Neocene  (Miocene)  a  large  fresh- 
water lake  occupied  at  least  the  lower  part  of  the  Snake  River  Val- 
ley, and  its  sediments  are  now  prominent  features  of  the  region. 
For  these  lake  beds  the  name  Payette  formation  is  proposed,  and 
their  age  is  determined  as  upper  Miocene.  This  formation  is  prob- 
abty  not  the  same  as  Cope's  Idaho  formation,  to  \fhich  a  Pliocene  age 
was  assigned  and  which  appears  to  be  connected  with  the  later  basalt 
flows.1 

The  extent  of  the  formation  is  shown  in  PI.  LXXXVII,  from  which 
it  is  seen  that  it  lies  in  front  of  the  Boise  Mountains  and  occupies  the 
whole  lowei*  part  of  the  ridge  between  the  Boise  and  the  Payette.  It 
extends  over  large  areas  to  the  north  of  the  Payette,  along  the  flood 
plains  of  the  Snake  River,  and  is  seen  to  occupy  vast  areas  in  Oregon 
between  the  mouth  of  the  Owyhee  River  and  Weiser,  where  the 
Snake  River  Canyon  begins.  On  both  sides  of  the  lower  Snake  River 
the  bluffs  of  the  Payette  formation  attain  a  height  of  over  800  feet. 
In  the  Payette  Valley  south  of  Emmett  the  sharply  defined  bluff  of 
Payette  beds  rises  600  feet  above  the  alluvium.  Smaller  masses, 
detached  by  erosion  or  uplifts,  lie  in  the  intermontane  valleys  as  far 
east  as  the  Idaho  Basin. 

Along  the  Boise  Mountains  the  Payette  beds  rest  against  the  irreg- 
ularly eroded  and  sharply  sloping  surface  of  the  granite,  and  the  top 
stratum  attains  a  height  of  4,100  feet.  A  total  thickness  of  1,000  feet 
is  exposed  near  Boise,  and  wells  bored  show  several  hundred  feet  of 
similar  strata  below  the  surface.  Over  the  larger  part  of  its  extent 
the  formation  lies  nearly  horizontal  or  dips  only  a  few  degrees.  Near 
the  mountains  dips  of  8°  to  10°,  generally  westward,  are  noted,  and  the 
smaller  detached  masses  in  the  intermontane  valleys  are  still  more 
disturbed,  generally  dipping  westward  at  angles  up  to  50°.  This  is 
particularly  marked  in  the  long  arm  of  sediments  of  the  Payette  for- 
mation filling  the  valleys  of  Horseshoe  Bend  and  Jerusalem,  on  the 
Payette. 

As  might  be  expected  from  the  character  of  the  land  mass  from 
which  the  sediments  were  obtained,  the  latter  consist  chiefly  of  granitic, 
light-colored  sands,  locally  cemented  by  hot-spring  deposits  to  hard 

1  From  the  results  of  more  extended  surveys  during  the  summer  of  1897,  it  has  become  evident 
that  the  Payette  and  Idaho  formations  represent  two  successive  stages  of  the  lake,  the  often 
deformed  shore-line  of  the  former  being  found  at  elevations  of  from  4,200  to  5,000  feet,  and  those 
of  the  latter  at  a  maximum  elevation  of  3,000  feet.  To  separate  the  deposits  of  the  two  forma- 
tions is  not  always  easy. 


LIN  DORK  N.I 


PAYETTE    FORMATION.  633 


sandstones  (as  at  Table  Mountain  near  Boise;  see  PL  LXXXVIII) 
or  clayey  semiconsolidated  sandstones.  Heavy  masses  of  conglomer- 
ates and  gravels  begin  to  appear  at  Table  Mountain,  and  reach  their 
greatest  development  opposite  the  mouth  of  Boise  River,  in  the  high 
ridge  extending  in  a  westerly  direction.  Purely  clayey  deposits  are 
rarer,  occurring  only  in  convenient  sheltered  locations  near  the  shore 
line  or  in  places  where  volcanic  eruptions  took  place.  The  basal  part 
of  the  formation  contains,  at  Horseshoe  Bend,  Jerusalem,  and  other 
localities  along  the  Payette,  small  coal  seams.  In  the  clay  accom- 
panying these  coal  seams  vegetable  remains  are  of  frequent  occur- 
rence. The  following  forms  were  identified  by  Professor  Knowlton: 

Two  miles  southeast  of  Marsh  post-office,  on  the  Payette,  is  a  small 
coal  prospect.  The  disturbed  beds  of  the  Payette  formation  lie  here 
on  a  sharply  sloping  surface  of  granite.  At  this  place  the  following 
forms  were  found,  together  with  many  new  species : 

Sequoia  angustifolia  ?  Lx. 
Quercus  consimilis  Newb. 
Acer  trilobatum  productum  ?  Heer. 

One  mile  southeast  of  Marsh,  along  the  road  to  Willow  Creek,  a  few 
hundred  feet  above  the  river,  is  an  outcrop  of  yellowish-gray  "chalk," 
or  diatomaceous  earth,  intercalated  in  the  Payette  beds  and  capped 
by  basalt.  In  this  the  following  forms  were  found,  in  an  excellent 
state  of  preservation : 

Salix  angusta  Al.  Br. 

Quercus  consimilis  Newb. 

Q.  simplex  Newby. 

Platanus  aspira  ?  Newb. 

From  Cartwright's  ranch,  on  Shafer  Creek,  4  miles  southeast  of 
Horseshoe  Bend  post-office,  the  following  forms  were  identified,  together 
with  several  new  species.  This  is  an  excellent  locality,  and  the  leaves 
embedded  in  a  dark  clay  shale  are  beautifully  preserved. 

Sequoia  angustifolia  Lx. 
Salix  angusta  Al.  Br. 
Ficus  ungeri  Lx. 

This  area  is  separated  from  the  main  one  by  a  small  ridge  of  gran- 
ite, but  that  the  two  formations  are  identical  admits  of  no  doubt. 
The  beds  are  here  disturbed,  dipping  west  at  20°  to  25°.  The  plants 
were  obtained  near  the  base  of  the  series,  of  which  about  800  feet  of 
alternating,  fairly  consolidated  shale  and  sandstone  are  exposed. 
The  elevation  is  3,500  feet. 

.Near  Idaho  City  another  detached  mass  of  lake  beds  is  preserved 
at  an  elevation  of  from  4,000  to  4,500  feet,  the  occurrence  of  which  is 
described  more  in  detail  in  Chapter  III.  From  the  middle  of  a  series 
800  feet  thick  the  following  plants  were  obtained: 

Sequoia  angustifolia  Lx. 

Ulmus  speciosa  Newberry. 

Betula  angustifolia  Newberry. 


634  IDAHO    MINING   DISTRICTS. 

From  these  data  Professor  Knowlton  draws  the  conclusion  that  the 
age  is  Upper  Miocene,  contemporaneous  with  the  flora  of  the  aurifer- 
ous gravels  and  the  lone  formation  of  California,  the  Lamar  flora 
of  the  Yellowstone  National  Park,  and  the  John  Day  formation  of 
Oregon.  The  paleobotanical  evidence  confirms  the  conclusion,  confi- 
dently drawn  from  the  field  work,  that  all  these  smaller  detached 
masses  of  lake  beds  are  of  practically  the  same  age. 

During  the  time  of  the  maximum  extension  of  the  Payette  Lake  its 
surface  stood  at  the  present  elevation  of  4,200  feet.  Its  deposits,  over 
1,000  feet  thick  near  the  shore,  rested  against  the  abrupt  slope  of  the 
Boise  Mountains,  and  filled  the  old  canyon  of  the  Boise  to  the  same 
depth.  The  canyon  must  have  formed  a  fiord,  the  branches  of  which 
reached  as  far  back  as  the  Idaho  Basin,  and  in  which  vast  quantities 
of  gravel  and  sand  accumulated.  Isolated  occurrences  of  well- washed 
gravel  on  the  summit  of  high  ridges  in  the  lower  Moore  Creek  drain- 
age, at  elevations  of  4,500  feet,  confirm  the  above  conclusions.  The 
data  are  not  at  present  sufficient  to  determine  the  extent  of  the  Payette 
Lake,  though  it  is  probable  that  it  was  confined  to  the  Snake  River 
Valley,  inclosed  on  the  west  by  the  Blue  Mountains  and  on  the  east 
by  the  divide  toward  the  Salmon  River. 

EARLY   NEOCENE   VOLCANIC    ACTIVITY. 

Near  the  base  of  the  Payette  formation  sheets  of  rhyolite  and 
rhyolite-tuff  occur,  but  this  eruption  was  of  limited  extent.  The 
best  exposures  are  found  near  Boise  and  in  the  Willow  Creek  mining 
district.  After  the  rhyolitic  eruptions  there  occurred  enormous  out- 
pourings of  basaltic  lavas,  distinctly  different  from  and  earlier  than 
the  Snake  River  basalts.  The  rocks  are  in  part  normal  basalts,  but 
have  usually  a  somewhat  andesitic  habit.  In  large  areas  the  outcrops 
generally  have  a  reddish-brown  color,  distinct  from  the  somber  black 
of  the  later  flows.  These  early  Neocene  eruptives  are  to  some  extent 
represented  near  Boise,  but  become  more  abundant  northward.  Many 
exposures  are  seen  along  the  lower  Payette  from  Marsh  post-office  to 
Horseshoe  Bend  and  Jerusalem  Valley,  and  the  conspicuous  sharp 
ridge  of  Squaw  Butte,  rising  just  north  of  the  Payette  above  the  lake 
beds  to  an  elevation  of  5,800  feet,  is  composed  entirely  of  these  older 
effusive  rocks.  Squaw  Butte  is  well  visible  from  the  railroad  near 
Nampa  and  Caldwell  as  a  rugged,  reddish-brown  peak,  contrasting 
•with  the  white  lake  beds.  The  evidence  shows  that  these  flows  were 
contemporaneous  with  the  deposition  of  the  Payette  beds,  and  are 
underlain  and  covered  by  sandstones.  In  some  places  they  break 
through  the  lower  lake  beds  and  metamorphose  them.  The  vents 
were  located  chiefly  along  the  margin  of  the  old  lake.  At  Jerusalem 
(see  PI.  LXXXIX)  arid  in  Squaw  Butte  the  whole  volcanic  series — in 
the  latter  place  consisting  of  countless  flows,  attaining  a  thickness  of 
several  thousand  feet — has  been  disturbed  and  uplifted,  and  now 


LINDOBEN.]  POST-PAYETTE    PHENOMENA.  635 

dips  to  the  west  at  angles  ranging  from  10°  to  35°,  the  monoclinal 
uplifts  vividly  recalling  those  in  eastern  Washington  described  by 
Professor  Russell.1  There,  however,  the  Miocene  beds  lie  only  on 
top  of  the  volcanic  flows  of  the  Columbia  formation,  while  here  they 
lie  both  below  and  above  similar  igneous  masses. 

On  both  sides  of  the  Snake  River,  from  Caldwell  to  Weiser  (near 
the  upper  edge  of  the  map,  PL  LXXXVII),  the  beds  do  not  contain 
much  evidence  of  volcanic  activity,  though  from  Parma  a  few  vol- 
canic buttes  are  visible  from  the  railroad,  far  to  the  west,  among  the 
lake  beds  in  Oregon.  But  a  few  miles  beyond  Weiser  the  white  bluffs 
of  lake  beds  begin  to  assume  red  or  orange  colors,  and  contain  streaks 
of  intercalated  tuffs.  The  valley  contracts,  and  at  the  entrance  of 
the  canyon  basaltic  rocks  appear,  partly  interstratified  with  the  lake 
beds,  partly  underlying  them.  Near  Huntington  the  deep  and  nar- 
row canyon  is  composed  entirely  of  basic  volcanic  rocks,  clearly  con- 
nected with  the  early  Neocene  lake  beds,  and  assuredly  different  from 
the  later  basalts  from  the  upper  valley.  How  far  down  this  volcanic 
canyon  extends  is  not  known. 

POST-PAYETTE   EROSION. 

After  attaining  its  highest  stage,  the  lake  was  drained  by  the 
establishing  of  the  present  course  of  the  Snake  River  below  Weiser. 
The  lake  receded  as  the  canyon  was  rapidly  cut  by  the  mighty  vol- 
ume of  water,  and  erosion  has  steadily  proceeded  since  the  end  of  the 
Miocene  or  the  beginning  of  the  Pliocene.  The  broad  valleys  of  the 
Boise,  the  Payette,  and  the  lower  Snake  were  eroded  in  the  soft  lake 
beds.  A  new  course  was  established  for  the  Payette  River,  which 
evidently  did  not  debouch  at  its  present  position  before  the  Payette 
epoch.  The  Boise  River,  on  the  contrary,  maintained  its  old  course. 
The  accumulated  gravels  were  scoured  out  from  its  canyon,  and, 
before  the  Pliocene  basaltic  eruptions,  its  channel  in  the  canyon 
was  deepened  nearly  to  its  present  level.  There  was,  however,  at 
least  one  temporary  check  in  this  process  of  draining.  For  a  consid- 
erable interval  of  time  the  lake  remained  stationary,  at  a  present 
elevation  of  from  2,800  to  3,000  feet.  The  deposits  and  basalt  flows 
of  this  epoch  are  regarded  as  late  Neocene  (Pliocene)  and  belong  to 
the  Idaho  formation  of  Cope. 

POST-PAYETTE   OROGRAPHIC   DISTURBANCES. 

Before  the  epoch  of  the  Pliocene  basalt  flows  the  sediments  and 
flows  of  the  Payette  formation  were  subject  to  some  disturbances, 
reaching  their  maximum  in  the  smaller  areas  in  the  intermontane 
valleys.  Certain  parts  of  the  series  acquired  a  slight  westerly  dip. 
More  intense  orographic  movements  took  place  at  Squaw  Butte  and  in 
the  Horseshoe  Bend  and  Jerusalem  valleys,  resulting  in  monoclinal 

i  Bull.  U.  S.  Geol.  Survey  No.  108,  1893,  p.  28. 


636  IDAHO    MINING    DISTRICTS. 

uplifts,  the  detailed  character  of  which  will  be  discussed  in  the  text 
accompanying  the  Boise  folio  of  the  Geologic  Atlas  of  the  United 
States.  Important  movements  also  took  place  along  the  Boise  Ridge, 
which  separates  the  Idaho  Basin  from  the  Payette  River,  and  it  is 
probable  that  it  has  undergone  an  extensive  uplift.  Over  the  larger 
part  of  the  area  no  orographic  movements  have  affected  the  beds. 

LATE   NEOCENE    BASALTS. 

When  the  lake  had  been  partly  drained,  vast  basaltic  eruptions 
began,  and  in  time,  intercalated  with  lake  beds,  filled  the  whole  of  the 
upper  Snake  River  Valley  from  the  base  of  the  Tetons,  near  the  Wyo- 
ming line,  to  a  point  near  the  confluence  of  the  Boise  and  the  Snake. 
Between  this  point  and  Weiser  no  basalts  are  seen.  The  basalt  flows 
lie  horizontal,  filling  the  plains  and  the  modern  canyons.  They  are 
also  distinguished  by  their  fresh  character,  black  color,  and  columnar 
structure.  The  aggregate  thickness  probably  never  exceeds  1,000 
feet,  and  is  ordinarily  much  less,  individual  flows  being  rarely  over 
100  feet  thick. 

As  already  indicated,  the  basalts  were  erupted  from  a  great  num- 
ber of  inconspicuous  craters,  both  in  the  plains  and  in  the  adjoining 
mountains.  Their  fluidity  was  remarkable,  continuous  flows  of  50 
miles  or  more  being  noted.  Where  the  Boise  River  emerges  from  the 
mountains  the  exposures  are  exceptionally  good.  There  are  three  or 
four  flows,  the  principal  ones  coming  down  from  the  South  Fork  of 
the  Boise.  The  deepest  flow  of  comparatively  small  volume  is  prob- 
ably the  oldest,  and  lies  but  a  few  feet  above  the  present  bed  of  .the 
river.  Deep  river  gravels  accumulated  on  this  flow,  and,  soon  after- 
ward, two  later  flows  came  down  the  Boise  River  and  filled  the  canyon 
near  the  mouth  to  a  depth  of  300  feet.  Beyond  the  mouth  the  basalt 
spreads  out,  and  its  surface  rapidly  sinks  westward.  Still  another 
basalt  flow,  about  75  feet  thick,  came  down  from  Moore  Creek  and 
joined  the  large  ones  at  the  mouth  of  the  main  river.  Above  the 
source  of  this  basalt  the  damming  resulted  in  terraces  and  bench 
gravels  now  lining  the  upper  valleys  of  Moore  Creek  and  Grimes 
Creek,  described  in  Chapter  III. 

POST-BASALTIC    EROSION. 

If  the  epoch  of  the  basaltic  flows  be  placed  at  the  very  close  of  the 
Neocene,  the  events  that  have  taken  place  since  then  must  be  referred 
to  the  Pleistocene.  Among  these  are  the  erosion  of  the  canyons  of 
Snake  River  and  its  tributaries  to  a  depth  of  from  200  to  700  feet  and 
the  deposition  of  extensive  flood  plains  and  terraces  along  the  lower 
Snake,  Boise,  and  Payette.  The  Boise  River  has,  in  Pleistocene  times, 
cut  through  the  300  feet  of  basalt  accumulated  at  the  mouth  of  its 
canyon,  and  thus  laboriously  regained  the  same  stage  it  occupied 
before  the  beginning  of  the  Payette  epoch.  The  direction  of  the  chan- 
nel has  gradually  changed.  During  the  Payette  epoch  it  had  a  nearly 


LINDGHEN.] 


RESUME    OF    GEOLOGICAL    HISTORY. 


637 


westerly  trend,  while  subsequent  events  have  more  and  more  forced 
it  in  a  northwesterly  direction.  PI.  LXXXVIII  illustrates  well  the 
present  condition  at  the  mouth  of  the  canyon — the  basalt  flow  cut  in 
two  and  the  two  Pleistocene  flood  plains  in  the  widening  valley  of  the 
river.  Pliocene  gravel  older  than  the  flood  plains  underlies  the  basalt. 
In  the  right  background  the  Miocene  sandstones  of  Table  Mountain 
are  shown,  while  the  background  at  the  extreme  right  shows  the  first 
granitic  hills  of  the  Boise  Ridge. 

Having  thus  traced  the  cycle  of  events  which  have  taken  place  in 
this  region  since  the  beginning  of  the  Neocene,  it  may  be  well  to 
rapidly  review  the  main  points  in  the  history. 

RESUME   OF   GEOLOGICAL   EVENTS  IN  THE   LOWER  SNAKE   RIVER 

BASIN. 


Pre-Neocene . 


Pre-Neocene  or  early  Neo 
cene  (Miocene) . 


Early  Neocene  ( Miocene ) , 
possibly  extending  over 
into  late  Neocene. 


Late  Neocene  (Pliocene) . . 


Pleistocene  ... 


/  The  depression  of  the  Snake  River  Valley  outlined  by 
I      orographic  movements. 

f  Long-continued  erosion,  dissecting  the  Boise  Moun- 
tains. 
f  Boise  Canyon  eroded  to  its  present  depth  at  its  mouth. 

Large  fresh-water  lake  occupying  Snake  River  Val- 
ley. 

Deposition  of  thePayette  formation  at  least  1,200  feet 
thick. 

Highest  level  reached,  4,200  feet  above  present  sea 
level. 

Eruptions  of  rhyolite  and  andesitic  basalts,  contem- 
poraneous  with  the  sedimentation. 

Orographic  disturbances  of  the  Payette  formation. 

Partial  drainage  of  the  lake  and  epoch  of  erosion 
excavating  the  valleys  of  the  Snake,  Boise,  and 
Payette  from  the  Payette  lake-beds. 

Basalt  flows,  filling  the  Snake  River  plains  and  the 
Boise  Canyon. 

Deposition  of  lacustrine  sediments  between  the  flows. 
(Idaho  formation.) 

Complete  draining  of  lake. 

f  Erosion  of  the  Snake  River  basalt  canyon  above  the 
confluence  with  the  Boise;  Boise  River  cuts  down 
through  the  basalt  to  its  present  depth. 

1^  Terraces,  up  to  100  feet  above  the  river,  and  present 
flood  plains  along  the  Lower  Snake,  Boise,  and 
Payette  rivers. 


CHAPTER    II. 
THE   ORE   DEPOSITS  IN   GENERAL. 

GENERAL    FEATURES. 

Throughout  the  Boise  Ridge  and  the  Idaho  Basin  the  primary  gold 
deposits  present  a  certain  similarity.  They  are  all  contained  in  gra- 
nitic rocks  or  associated  dikes.  They  are  all  either  fissure  veins  or 
impregnations  connected  with  fissures.  Nearly  all  of  these  fissures 
have  a  direction  ranging  from  east- west  to  northeast-southwest,  the 
chief  exceptions  to  this  rule  being  "found  in  the  Black  Hornet  district. 
The  dip  is  ordinarily  to  the  south  at  angles  of  from  45°  to  89°,  but  in 
the  Willow  Creek  and  Rock  Creek  districts  similar  dips  to  the  north 
are  found.  The  prevailing  direction  of  the  fissures  is  the  same  as 
that  of  an  often  well-developed  system  of  joint  planes  commonly  seen 
in  the  Boise  Ridge.  Finally,  the  ores  are,  on  the  whole,  of  a  similar 
character,  consisting  chiefly  of  auriferous  pyrite,  arsenopyrite,  zinc- 
blende,  and  galena  in  a  gangue  of  quartz  or,  more  rarely,  calcite. 
The  fresh  ores  from  deeper  levels  contain  a  variable  percentage  of  free 
gold.  Rarely,  however,  is  more  than  60  per  cent  of  the  total  value 
caught  on  the  amalgamating  plates.  Gold  predominates  largely  in 
the  value  of  the  ore,  though  seldom  by  weight,  for  in  the  ordinary 
ores  the  weight  of  the  silver  considerably  exceeds  that  of  the  gold. 
The  alteration  of  the  country  rock  in  the  vicinity  of  the  veins  is 
throughout  of  the  same  character. 

ALTERATION    OF    THE    COUNTRY    ROCK. 

A  marked  change  appears  in  the  rock  in  the  vicinity  of  the  veins. 
The  dark  constituents,  biotite  and  hornblende,  are  bleached  or  disap- 
pear, and  the  feldspar  is  altered  to  a  soft,  white,  opaque  material, 
only  the  quartz  remaining  unaltered.  Besides  abundant  iron  pyrite, 
arsenopyrite  also  appears  in  small,  scattered,  perfect  crystals.  The 
width  of  the  altered  zone  may  be  from  a  foot  up  to  50  or  60  feet. 
This  alteration  of  the  country  rock  has  been  noted  by  Messrs.  George 
H.  Eldridge,1  J.  B.  Hastings,2  and  F.  D.  Howe,  but  has  ordinarily 
been  described  as  kaolinization.  The  soft,  white  substance,  which 
often  has  a  greasy  feel,  is  also  referred  to  by  the  miners  as  "talc." 
This  change  in  appearance  and  composition  is  without  the  slightest 

1  Sixteenth  Ann.  Rep.  U.  S.  Geol.  Survey,  Part  II,  1895,  pp.  225,  252. 

2  Idaho  Mining  News,  Vol.  L,  No.  1,  p.  15. 
638 


LINDGRKN.]  ALTERATION    OF    THE    COUNTRY    ROCK.  639 

doubt  directly  due  to  the  chemical  action  of  the  solutions  from  which 
the  mineral  content  of  the  vein  was  deposited.  The  process  consists  in 
a  sericitization.  or  replacement  of  the  ferromagnesian  silicates,  feld- 
spar, partly  also  the  quartz,  by  sericite,  a  fine-fibrous  or  felted  variety 
of  white  mica.  In  composition  it  is  a  hydrous  silicate  of  aluminium 
and  potassium,  probably  identical  with  muscovite.  In  many  places  a 
carbonatization,  or  replacement  by  carbonate  of  lime  and  magnesia, 
goes  on  at  the  same  time,  and  sulphides,  chiefly  pyrite  and  arseno- 
pyrite,  rarely  other  minerals,  are  usually  also  formed  in  the  rock 
as  minute  and  perfect  crystals.  It  is  certain  that  this  metasomatic 
process  is  a  common  one  in  fissure  veins,1  audits  chemical  character 
is  very  different  from  kaolinization.  Kaolin,  in  fact,  is  a  product 
not  ordinarily  found  on  the  mineral  veins,  and  talc  occurs  still  more 
rarely. 

This  altered  granite,  together  with  the  ore  and  gangue  occurring  in 
seams  or  veins  through  it,  constitutes  what  miners  term  a  "ledge"  and 
' '  ledge  matter. "  This  may  be  many  feet  wide,  and  the  paying  ore  may, 
and  in  fact  does  usually,  form  only  a  small  portion  in  width  of  the 
ledge  matter.  The  altered  country  rock,  though  often  well  filled  with 
pyrite  and  arsenopyrite,  is  ordinarily  very  poor,  containing  at  most 
one  or  two  dollars  in  gold.  Exceptionally  it  contains  enough  gold  to 
be  considered  an  ore,  but  generally  only  when  adjoining  rich  vein 
filling,  and  large  ore  shoots;  even  then  it  constitutes  only  second-class 
ore,  and  its  sulphides  are  much  poorer  than  those  in  the  vein  proper. 
It  rarely  contains  any  free  gold.  As  examples  a  few  typical  rocks  of 
this  kind  may  be  described. 

The  altered  dioritic  granite  from  the  Checkmate  mine,  Willow  Creek 
(88  Boise  sheet  collection),  is  a  granular,  white,  soft  rock,  consisting 
of  quartz  grains,  white  earthy  grains  replacing  the  feldspar,  a  few 
foils  of  pale-yellowish  mica  and  abundant  small  and  perfect  crystals 
of  pyrite,  showing  the  combination  GO  0  GO,  GO  0  2,  and  a  few  small  prisms 
of  arsenopyrite.  A  few  narrow  seams,  lnnn  wide,  traverse  the  rock  and 
carry  only  blende  and  galena.  The  microscope  shows  quartz  grains 
with  undulous  extinction,  which  contain  in  places  a  few  shreds  of 
sericite,  but  are  on  the  whole  hardly  attacked  by  any  metasomatic 
process.  There  are  a  few  larger  muscovite  foils,  which  evidently  rep- 
resent the  biotite  of  the  fresh  rock.  The  space  between  the  quartz 
grains  is  filled  by  a  fine-felted  sericite  mass,  which  incloses  nearly  all 
of  the  idiomorphic  pyrite.  Intergrown  with  and  inclosed  by  the  pyrite 
is  a  little  brown  zinc  blende  and  galena  in  small  anhedral  grains ;  one 
crystal  of  arsenopyrite  was  also  noted.  No  calcite  was  found.  This 
rock  occurs  close  to  a  rich  ore  body,  but  an  assay  of  it  gave  only  0. 1 
ounce  of  gold  and  0.5  ounce  of  silver  per  ton.  The  total  replacement 

1  For  studies  of  the  metasomatic  processes  of  fissure  veins  by  the  author,  see  Fourteenth  Ann. 
Kept.  U.  S.  Geol.  Survey,  Part  II,  pp.  243-284,  and  Seventeenth  Ann.  Rept.U.  S.  Geol.  Survey, 
Part  II,  p.  144;  also  Bull.  Geol.  Soc.  Am.,  Vol.  VI,  p.  221. 


640 


IDAHO    MINING   DISTRICTS. 


of  the  feldspars  and  ferromagnesian  silicates  and  the  immunity  of 
the  quartz  is  noteworthy. 

From  the  Silver  Wreath  tunnel,  Willow  Creek  district,  Boise 
County,  two  rocks  were  collected,  analyses  of  which  are  given  below. 
The  first  is  a  perfectly  fresh  granitic  rock,  the  ordinary  country  rock 
of  the  district.  The  second,  occurring  only  a  few  feet  away,  is  the 
same  granite  altered  by  the  vein-forming  agencies,  and  a  comparison 
between  the  two  will  show  the  character  of  the  process.  Both  rocks 
are  unaffected  by  atmospheric  agencies. 

Analyses  of  rocks  from  Silver  Wreath  tunnel. 
[Analyst,  George  Steiger.] 


I. 

II. 

SiO2  

65.23 
.66 
16.94 
1.60 
1.91 
trace 
3.85 
.19 
1.31 
3.02 
3.57 
.18 
.88 
.19 
none 
none 
.25 

66.66 
.49 
14.26 
.67 
2.41 
trace 
3.37 
none 
.95 
4.19 
none 
.36 
2.16 
.17 
none 
.95 
3.67 

TiO2                                                  -  . 

A1,O3  ..              ..            

FeiO3      

FeO         .                         .... 

MnO        -  

CaO    

BaO         .            .     .          

MgO             

K,O 

Na,O  

H»O  below  100°    

H2O  above  100°  

PA 

SO, 

s           .                

CO*  -  -  

Less  O 

99.78 

100.  31 
.24 

100.  07 

I.  79  Boise  collection;  fresh  granitic  rock. 
II.  80  Boise  collection;  altered  granitic  rock. 

The  unaltered  rock  is  light  gray  and  coarse  grained,  the  average 
size  of  the  constituents  being  5mm  to  6mm.  With  the  naked  eye,  white 
plagioclase,  reddish  orthoclase,  biotite,  titanite,  and  quartz  may  be 
distinguished.  Under  the  microscope  the  quartz  proves  to  be  very 
abundant  and  is  slightly  crushed.  The  plagioclastic  feldspars  pre- 
dominate and  occur  generally  in  anhedrons,  more  rarely  in  roughly 
prismatic  forms.  Symmetric  extinctions  show  a  maximum  of  10°.  A 


LINDOEEN.]  COMPOSITION   OP   THE    COUNTRY    ROCK.  641 

little  orthoclase  lies  between  the  plagioclase  grains.  The  biotite 
occurs  in  small  foils  of  brownish  yellow  color.  Magnetite  occurs 
sparingly.  Titanite  is  much  more  abundant,  occurring  in  large  crys- 
tals or  anhedrons,  sometimes  wedge-shaped.  It  includes  small  feld- 
spar grains,  but  its  crystals  also  project  into  larger  feldspar  grains. 
The  structure  of  the  rock  is  eugranitic. 

An  approximate  calculation  of  the  analysis  of  the  fresh  rock  (I) 
may  be  made  in  the  following  manner :  On  the  basis  of  a  preliminary 
calculation  and  estimate  there  is  about  15  per  cent  of  biotite  present. 
For  this  1.20  per  cent  potassa  was  subtracted.  The  baryta  is  calcu- 
lated as  hyalophane,  which  necessitates  a  deduction  of  0.12  per  cent 
more  of  potassa.  The  remainder  is  calculated  as  orthoclase.  The 
lime  needed  for  calcite,  titanite,  and  apatite  is  subtracted  from  the 
total  lime.  The  amount  of  magnetite  is  estimated.  Finally  biotite 
and  quartz  remain.  From  the  amounts  of  the  bases  in  this  remainder 
it  is  estimated  that  there  is  25  per  cent  free  quartz  present. 

SiO2 - 6.51 

A1,O3 - 1.85 

K,0 -  1.70 

KAlSi3O3 10.06 

SiOi - - 20.78 

.     AI2O3 ---     5.90 

-- ---- --     3.57 


NaAlSi3O3 --.. 30.25 

SiO* --- 6.00 

A12O3 --- 5.09 

CaO..  2.79 


CaAl2Si.2O8  .....  ..  ......  ______  .....  ________  ..........  13.88 

SiO2...  .........................  .  ..........  _________       .59 

A12O3  ......  .  .....  -.  .....  ____________________________       .25 

BaO  ......  .......  -.  .....  ___________  .......  -  .........  19 

K20  ...................  --  ..........  ---  •  --       -12 

Ba  Al,Si2O82KAlSi2O8__.-  .......  .  .....  ..  .............     1.15 

PA—  -  ..................  ---------  ................  19 

-.--  ......................  -  ........  ---  .........  25 


Apatite  .......  .  ...............................  -------       .44 

Ti02  .....  .  ..........  -  ..........  -  ...............  ---       -66 

Si08  _____  ..................  _______  ............  -  .......  50 

CaO  ........  .  ........  -.--  .............  _____  .49 

Titanite  ......................................  -  .....     1-65 

FeO  ........  .......  .  .................  -  ............  —       -20 

Fe3O3  ______________________  .......... 

Magnetite  ............  .  ...........  -  ...............          -61 

CaO  ............................  .....................  32 

C02  .....  i  ..............  -  ...........................     -.25 

Calcite  .  _____  .....  .  ...........................  ---- 

Quartz.  .....  .  .......................................  25.00 

18  GEOL,  PT  3  -  41 


642  IDAHO    MINING    DISTRICTS. 

SiO2 5.85 

.ALA- - 3.85 

Fe203- - • --  i'19 

FeO.... - 1-71 

MgO 1.31 

K3O --- -- 1-20 

H20..                                                      -88 


Biotite..- ---  15.99 

Hygroscopic  water . -.-       .18 

Total - 99.78 

The  biotite  would  have  the  following  composition: 

Si0.2 --- - 36.59 

A120,  -- --- 24.08 

Fe,O3 ---- — 7.44 

FeO 10.69 

MgO... - 8.19 

K;O._.- - '---  7.51 

H2O..                                                                                     5.50 


100. 00 

The  water  is  somewhat  too  high,  no  doubt  due  to  the  fact  that  chlo- 
rite and  other  decomposition  products  are  present. 

According  to  mineralogical  composition,  habit,  and  chemical  com- 
position, this  rock  corresponds  closely  to  the  granodiorite  of  the  Sierra 
Nevada,  the  only  difference  being  that  it  contains  no  hornblende, 
which  in  the  granodiorite  is  as  a  rule  abundant.  It  thus  occupies  a 
position  between  a  quartz-mica-diorite  and  a  granite.  However,  as  it 
grades  imperceptibly  over  into  more  normal  granites,  it  has  not  been 
thought  worth  while  to  segregate  it  from  that  rock.  The  plagioclase 
in  the  Willow  Creek  rock  is,  according  to  the  ratio  between  albite  and 
anorthite,  Ab2An,  or  a  basic  oligoclase. 

The  second  rock  (80  Boise  collection)  is  grayish  white,  granular, 
with  a  clearly  apparent  granitic  habit.  It  consists  of  quartz  grains  of 
about  the  same  size  as  in  the  fresh  rock,  while  a  greenish-gray  com- 
pact mass  replaces  the  feldspar  and  has  a  hardness  of  about  3.  The 
biotite  is  replaced  by  a  dull- white  micaceous  mineral.  Small  crystals 
of  pyrite  abound,  and  the  rock  is  also  traversed  by  a  few  small  quartz 
veins.  In  a  few  places  small  grains  of  zinc  blende  are  seen. 

Under  the  microscope,  large  grains  of  quartz  with  undulous  extinc- 
tion are  noted.  Between  them  lies  a  fine-felted  mass  of  sericite 
fibers,  calcite  grains,  and  in  places  a  little  fine-grained  quartz.  No< 
feldspar  remains,  though  occasionally  the  outlines  of  the  grains  may 
still  be  noted.  In  places  larger  muscovite  foils  appear,  evidently 
representing  the  original  biotite.  The  quartz  is  in  many  places 
attacked  by  sericitization,  fibers  and  tufts  of  sericite  and  calcite 
developing  in  it  or  projecting  into  it  from  the  surrounding  sericite 
mass.  Titanite,  extremely  abundant  in  the  unaltered  rock,  is  con- 


LINDGREN.]  COMPOSITION   OF   ALTERED    GRANITE.  643 

verted  into  a  milky  opaque  mass,  composed  of  a  great  number  of 
small  crystals.  The  also  abundant  apatite  is  not  attacked  at  all  by 
any  metasoinatic  process.  The  idiomorphic  pyrite  is  chiefly  contained 
in  the  altered  feldspars,  but  also  included  in  the  quartz.  When  the 
pyrite  crystals  are  larger  the  quartz  in  the  vicinity  often  shows  very 
strong  undulous  extinction,  but  some  small  perfect  crystals  also  lie 
in  the  fresh,  unchanged  quartz,  usually  attached  at  one  side  to  a 
bunch  of  sericite  fibers.  An  assay  of  this  rock  gave  0.05  ounce  of 
gold  and  0.5  ounce  of  silver  to  the  ton. 

Analysis  II  shows  the  composition  of  the  altered  granite.  The 
chemical  change  is  on  the  whole  slight.  Silica  shows  a  small  increase, 
alumina  a  decrease ;  a  very  slight  decrease  is  also  noted  in  the  iron 
oxides,  lime,  magnesia,  and  titanic  acid,  while  the  whole  of  the  soda 
and  the  baryta  has  been  carried  away,  and  the  percentage  of  potash 
has  been  considerably  augmented.  Sulphur  and  carbon  dioxide  have 
been  introduced,  and  the  quantity  of  chemically  combined  water 
has  been  increased. 

With  the  aid  of  the  data  furnished  by  the  microscopic  investiga- 
tion, the  analysis  may  be  calculated  as  follows.  The  lime  has  been 
calculated  as  carbonate,  excepting  that  necessary  for  apatite  and 
titanite,  the  whole  of  the  magnesia  likewise  as  carbonate,  and  as 
much  of  the  ferrous  oxide  as  the  remaining  carbon  dioxide  would 
permit.  The  remainder  is  sericite  and  quartz.  The  amount  of  free 
quartz  has  been  estimated  according  to  the  quantity  of  oxides 
available  for  sericite. 

S 95 

Fe._  .83 


Pyrite 1.78 

P2O, 17 

CaO.-  .22 


Apatite  ... 

.39 

TiO; 

.49 

SiO2 

.33 

CaO                       

....                     .46 

Titanite  

1.28 

CaO  

2.69 

CO2                    -                   

2.11 

Calcium  carbonate  

4.80 

MgO                -          .  .            .... 

0.95 

CO,  . 

1.01 

Magnesium  carbonate 
FeO 

CO,  .. 


Ferrous  carbonate 1.45 

Quartz 42.00 


644  IDAHO    MINING    DISTRICTS. 

SiO* 24.33 

A1203 - -.. -- - 14.26 

Fe203---- 67 

FeO .44 

K20 4.19 

H20 ---       2.16 

Sericite.. 46.03 

Hygroscopic  water ... .36 

Total 100.07 

The  sericite  would  have  the  following  composition : 

SiO* - 52.82 

A1203 30.96 

Fe2O3 1.46 

FeO 96 

K20 9.10 

H3O._  4.70 


100. 00 

The  altered  wall  rock  from  the  Black  Hornet  mine  (60,  63  Boise 
sheet  collection)  is  a  grayish- white,  very  quartzose  rock  impregnated 
with  small  grains  and  crystals  of  arsenopyrite.  Though  adjoining 
ore  contained  from  $10  to  $20,  it  was  found  upon  assay  to  contain 
neither  gold  nor  silver  in  appreciable  quantities.  Under  the  micro- 
scope No.  60  appears  as  a  crushed  granite  or  coarse  granite-porphyry. 
The  quartz  grains  are  converted  into  coarse  aggregates;  the  unstri- 
ated  feldspar  is  filled  with  sericite  fibers  and  grains  of  arsenopyrite, 
some  of  which  have  a  little  adhering  chlorite.  No.  63  contains  unal- 
tered idiomorphic  andalusite,  besides  crushed  large  quartz  grains  and 
sericitized  microperthite,  and  also  a  little  soda-lime-feldspar.  Scat- 
tered grains  of  pyrite  are  associated  with  foils  of  sericite. 

The  ore  of  the  Black  Hornet  consists  of  massive  quartz  with  inclosed 
sulphides.  The  preponderating  quartz  is  granular  and  shows  strong 
evidence  of  pressure.  The  ores  consist  of  small,  perfect  crystals  of 
arsenopyrite  and  anhedral  grains  of  dark-brown,  scarcely  translucent 
zinc  blende;  inclosed  in  the  latter  are  many  small,  distinct  foils  of 
sericite.  Smaller  shreds  of  this  mineral  are  also  scattered  through 
the  quartz. 

The  granite  and  porphyries  adjoining  the  veins  of  the  Idaho  Basin 
are  altered  in  a  similar  manner.  Sericitization  always  takes  place, 
and  is  often  accompanied  by  the  formation  of  carbonates.  A  specimen 
from  a  seam  in  the  hanging  wall  of  the  Boulder  mine  (19  Idaho  Basin 
sheet  collection)  consists  of  a  quartz  vein  2-g-  inches  wide,  of  which  1 
inch  is  pure  quartz  and  the  rest  quartz  with  much  finely  divided  iron 
pyrite.  This  vein  is  inclosed  in  a  greenish- white,  bleached  granite, 
impregnated  with  a  little  pyrite  and  arsenopyrite. 

An  assay  of  the  quartz  vein  gave  2.25  ounces  of  gold  and  1  ounce 
of  silver  to  the  ton,  or  a  total  value  of  $47.21.  An  assay  of  the 


LINDGBEN.]  SILICIFIC  ATION.  645 

altered  granite  immediately  adjoining  this  piece  gave  only  a  trace  of 
gold  and  silver.  Under  the  microscope  the  altered  granite  is  seen  to 
contain  large,  partly  crushed  quartz  grains.  The  feldspar,  which  is 
partly  orthoclase,  partly  a  soda-lime-feldspar,  is  filled  with  sericite 
foils,  chiefly  developing  on  the  cleavage  planes,  and  a  few  grains  are 
almost  totally  replaced  by  this  material.  A  few  larger  muscovite  foils 
probably  represent  the  altered  biotite.  No  calcite  is  present. 

The  diorite-porphyrites  and  quartz-diorite-porphyrites  of  the  Gold 
Hill  and  Pioneer  mine  at  Quartzburg  show  a  similar  alteration,  chiefly 
consisting  in  a  conversion  of  the  hornblende  and  biotite  to  muscovite 
foils,  calcite,  and  perhaps  also  pyrite,  while  there  is  a  great  develop- 
ment of  fine-felted  sericite  in  'the  feldspar  phenocrysts  and  in  the 
groundmass.  The  abundant  pyrite  is  in  sharp  cubes,  usually  lined 
with  sericite  foils.  Aggregates  of  secondary  quartz  also  develop  in 
places. 

Silicification. — Mr.  S.  F.  Emmons,  in  his  studies  of  the  mineral  depos- 
its of  Colorado  and  other  parts  of  the  Rocky  Mountains,  has  admirably 
and  with  deserved  emphasis  brought  out  the  fact  that  replacement  is 
a  process  to  which  many  deposits  owe  their  origin,  and  that  it  plays  an 
important  part  in  almost  all  deposits  caused  by  mineral-bearing  waters. 
Carried  away  with  the  importance  and  interest  of  these  results,  many 
geologists  and  mining  engineers  have,  however,  extended  the  theory 
of  replacement  beyond  its  proper  bounds,  and  speak  of  every  vein- 
filling  and  even  of  veins  of  solid  white  quartz  as  products  of  replace- 
ment. Against  this  view  a  strong  protest  should  be  entered.  In  this 
connection  it  may  be  of  interest  to  consider,  briefly,  the  processes  by 
which  silicification  may  be  produced. 

In  the  case  of  ores  consisting  of  carbonates  there  may  often  be  some 
difficulty  in  deciding  what  is  filling  and  what  is  replaced  country 
rock,  for  carbon  dioxide  and  alkaline  carbonates  are  very  strong  sol- 
vents, attacking  easily  nearly  every  one  of  the  rock-forming  minerals 
and  forming  pseudomorphs  after  them.  The  carbonates  may  replace 
a  rock  completely,  wholly  changing  both  composition  and  structure. 
As  an  instance  may  be  cited  the  coarse-grained  mixture  of  carbonates 
and  mariposite  (fuchsite — a  chromium  mica)  resulting  from  the 
replacement  of  the  serpentine  along  the  Mother  lode  of  California. 

As  to  quartz,  the  conditions  are  wholly  different.  A  solution  of 
silica  is  comparatively  inert  and  does  not  easily  attack  any  of  the 
rock-forming  silicates.  Silicification  may  take  place  by  two  greatly 
differing  processes:  (1)  Cementation,  or  filling  of  the  interstices  of 
porous  or  shattered  rocks  by  quartz  deposited  from  solutions;  (2) 
metasomatic  silicification,  or  a  substitution  of  silica  for  other  miner- 
als, the  silica  either  being  produced  by  the  alteration  of  the  original 
minerals  or  deposited  pari  passu  with  the  dissolving  of  the  original 
mineral  by  active  reagents  in  the  waters  causing  the  metasomatic 
action. 


646  IDAHO    MINING    DISTRICTS. 

The  first  process  is  often  observed  in  the  silicification  of  various 
sedimentary,  porous  rocks,  chiefly  sandstones  or  tuff  or  porous  igne- 
ous rocks,  such  as  certain  trachytes  and  andesites.  Silicification  by 
the  cementation  of  shattered  rock  masses  by  silica  is,  of  course,  a 
common  occurrence  in  and  near  quartz  veins.  But  silicification  by 
replacement  is  a  less  common  process,  and  is  observed  chiefly  in  the 
case  of  easily  soluble  rocks,  such  as  limestone  or  calcareous  shales, 
when  it  results  in  fine-grained  or  cryptocrystalline  aggregates  of 
silica.  In  the  metasomatism  of  bodies  of  massive  rocks  penetrated 
by  chemically  active  solutions  silica  is  formed  in  many  ways,  as  by 
the  carbonatization  of  silicates  and  sericitization  of  the  feldspars, 
and  if  no  open  spaces  are  available  much  of  this  free  silica  will  be 
deposited  within  the  rock,  usually  as  fine-grained  aggregates  more 
or  less  mixed  with  opal  and  chalcedonite.  If  no  material  were  added 
the  final  result  of  this  would  not,  however,  be  a  silicification,  but 
merely  an  increase  in  the  total  free  quartz  of  the  rock.  But  in  case 
the  rock  mass  is  cut  by  fissures  it  appears  that  most  of  the  resulting 
free  silica  is  not  deposited  in  the  rock,  but  finds  its  way  out  in  the 
open  ducts,  where,  if  the  solution  is  supersaturated,  it  will  be  depos- 
ited. In  fact,  in  the  metasomatic  processes  in  the  ordinary  igneous 
rocks  adjoining  gold-quartz  veins,  late  investigations  have  shown 
that  certain  elements  are  added  to  the  rock,  while  others,  notably 
silica,  are  frequently  subtracted,  to  be  carried  away  or  deposited  in 
available  open  spaces. 

As  for  the  other  possible  process  of  silicification,  or  a  dissolving  of 
the  original  mineral  and  a  deposition  of  silica  pari  passu,  it  occurs 
chiefly  in  easily  soluble  minerals,  such  as  calcite.  In  case  of  the 
ordinary  rock-forming  silicates  it  is  apparently  not  common.  The 
resulting  silica  is  generally  in  the  form  of  fine,  cryptocrystalline 
aggregates.  Rocks  silicified  by  either  of  these  metasomatic  processes, 
or  by  a  combination  of  both,  may  occur,  but,  so  far  as  the  writer's  ex- 
perience goes,  are  not  often  encountered  as  wall  rocks  of  auriferous- 
quartz  veins.  But  neither  of  these  processes  can  have  produced  the 
massive,  white,  coarse-grained  quartz  of  gold  veins  belonging  to  the 
normal  type.  This  quartz,  which  contains  native  gold  and  sulphides, 
shows,  under  the  microscope,  a  peculiar,  coarsely  granular  structure, 
the  grains  being  partly  bordered  by  crystallographic  surfaces.  This 
structure  could  have  been  developed  only  by  free  crystallization  in 
open  spaces.  It  is  scarcely  necessary  to  call  attention,  in  addition,  to 
the  frequency  of  comb  structure,  etc. ,  proving  also  the  same  kind  of 
origin.  This  does  not  necessarily  mean  that  all  large  bodies  of  quartz 
have  been  deposited  in  an  open  space,  as  large  as  the  volume  of  quartz 
now  is.  Repeated  openings  of  the  fissure  have  doubtless  often  taken 
place. 

In  nature  the  complication  of  the  fissure  veins  is  often  great,  and 
it  is  clear,  in  fact,  that  it  must  be  so,  for  the  walls  are  often  shattered, 


LINDGBKN.]  VEIN   STRUCTURE.  647 

resulting  in  alteration  of  the  country  rock  and  deposition  of  a  net  of 
quartz  in  the  interstices.  Ground-up  mud  often  fills  the  fissure,  and 
the  result  of  the  action  of  the  solutions  on  this  will  be  a  mass  of  grains 
of  altered  rock,  cemented  as  in  a  sandstone  by  quartz. 

STRUCTURE   OF   THE   VEINS. 

The  existence  of  fissure  veins  is  primarily  due  to  one  or  more  fault 
planes,  fissures  or  seams  forming  ducts  for  ore-bearing  solutions. 
The  latter  have  then  produced  the  materials  now  forming  the  vein, 
which  may  be  divided  into  (1)  vein-filling,  or  minerals  deposited  in 
the  open  spaces  along  the  fissure,  and  (2)  metasomatically  altered 
country  rock.  Though  it  is  not  in  every  case  possible  to  strictly  sep- 
arate the  two  classes,  as  a  rule  it  can  be  done.  Many  of  the  puzzling 
questions  in  regard  to  veins  and  vein-filling  may  be  solved  if  this  dis- 
tinction is  made  and  carefully  applied.  Products  of  attrition,  often 
present  in  quartz  veins,  belong,  as  a  rule,  to  the  second  class  of 
materials.  The  vein-filling  which  ordinarily  constitutes  the  ore  is 
composed  of  various  sulphides  with  a  gangue  of  more  or  less  quartz 
and  calcite.  Naturally  it  occurs  chiefly  along  the  fault  planes  and 
seams.  At  Willow  Creek,  for  instance,  the  seams  consist  of  nearly 
solid  sulphides  with  a  little  quartz  and  calcite.  These  largely  rep- 
resent filling,  but  are  probably,  to  a  minor  extent,  formed  by  replace- 
ment of  the  country  rock  immediately  adjoining  the  fault  planes. 
At  other  localities,  as  at  Black  Hornet  and  Shaw  Mountain,  the  ore 
consists  of  quartz-filling  exclusively,  with  scattered  grains  and  masses 
of  rich  sulphides  and  native  gold. 

The  typical  fissure  vein  may  be  regarded  as  a  single  break  or 
fissure  along  which,  through  faulting,  more  or  less  continuous  open 
spaces  were  formed  and  subsequently  filled  with  ore.  On  both  sides 
of  this  filling  there  is  a  gradually  fading  zone  of  alteration  of  the 
country  rock. 

In  many  regions  the  typical  simple  fissure  vein  is  relatively  rare. 
The  country  rock  may  be  cut  by  one  or  several  fault  planes,  along 
which  only  small  open  spaces  have  formed  and  around  which  there  is  a 
wide  belt  of  altered  country  rock.  The  ore,  then,  mainly  accumulates 
along  these  planes,  largely  by  filling,  partly,  also,  by  metasomatism 
of  the  adjoining  rocks.  Again,  there  may  be  a  shattered  zone  adjoin- 
ing one  or  more  fault  planes.  The  rock  is  then  traversed  by  a  com- 
plicated system  of  seams,  and  large  areas  of  the  country  rock  may  be 
altered.  In  this  case,  again,  the  seams  generally  contain  the  gold 
and  the  whole  seamed  rock  mass  may  form  a  large  ore  body  of  low 
grade. 

On  PI.  XC  (p.  650)  a  few  types  of  the  fissure  veins  occurring  in  this 
region  are  diagrainniatically  represented. 


648  IDAHO    MINING    DISTRICTS. 

MINERAL   DEPOSITS   OF   POST-NEOCENE   AGE. 

As  has  been  explained  before,  there  is  every  reason  to  believe  that 
all  of  the  more  important  ore  deposits  antedate  the  Payette  formation, 
or  that,  in  other  words,  they  are  pre-Miocene.  But  there  is  also  some 
evidence  of  a  later  period  of  ore  deposition,  although  of  less  impor- 
tance, which  occurred  after  the  early  Neocene  eruptions,  and  which 
may  be  going  on  in  depth  even  at  the  present  time  by  means  of  the 
hot  ascending  spring  waters  found  at  several  places  in  this  region. 

The  Neocene  rhyolite  area  occurring  on  the  Idaho  City  road  3  miles 
from  Boise  is  somewhat  altered  in  places  and  is  stated,  on  reliable 
authority,  to  contain  $1  per  ton  in  silver  and  a  trace  of  gold.  A 
Neocene  sandstone  with  veins  of  opal,  occurring  near  this  area  along 
the  road,  was  assayed  and  found  to  contain  0.50  ounce  of  silver  per 
ton.  The  knob  of  partly  altered  augite-andesite  near  the  penitentiary 
at  Boise  was  assayed  and  found  to  contain  0.05  ounce  of  gold  and 
0.50  ounce  of  silver  per  ton,  a  total  value  of  $1.38. 

The  Neocene  basalt  at  the  mouth  of  the  canyon  of  Jackass  Creek, 
Jerusalem  Valley,  contains  a  quartz  vein  which  is  stated  to  assay 
about  $4  in  gold  and  silver. 


PLATE   XC. 

649 


PLATE  XC. 

1.  Simple  fissure  vein  with  one  fault  plane  and  with  quartz  filling.    Altered 

country  rock  on  both  sides.     Filling  only  constitutes  the  ore. 

2.  Complex  fissure  vein  with  three  fault  planes.     Rich  ore  as  filling  along  narrow 

openings,  partly  also  by  alteration  of  country  rock  immediately  adjoining 
fissures.    Less  altered  country  rock  between  and  beyond  the  fault  planes. 

3.  Simple  fissure  vein  without  large  open  spaces.    Ore  partly  as  filling,  partly  as 

altered  country  rock.     Less  altef  ed  country  rock  on  both  sides  of  fault  plane. 

4.  Complex  fissure  vein  with  two  fault  planes,  along  which  quartz  is  deposited  as 

filling.    Wide  sheeted  and  altered  zone  between  the  two  fissures. 

5.  Irregularly  shattered  zone  between  two  fault  planes.     Quartz  filling  in  seams 

and  cracks.    Extensive  alteration  of  country  rock  between  fault  planes. 

6.  Single  fissure  in  foot  wall  of  porphyry  dike.    Dike  traversed  by  stringers  from 

hanging  wall,  shattered  and  extensively  altered.     Quartz  filling  in  fissure 
and  seams.     Rich  ore  in  quartz  vein.    Altered  porphyry  constitutes  low- 
grade  ore. 
650 


U.    8.    GEOLOGICAL  SURVEY 


EIGHTEENTH  ANNUAL  REPORT      PART  III      PL.  XC 


/••:/  \--/\-'-/-'-r--#:- 

•tft^^y^ 

::iiiW^MM 

•••m+^^:m-: 

.F.-Vii 


iiSif; 


Scale. 


.     .    '?  feel- 


TYPES  OF  GOLD-BEARING  FISSURE  VEINS. 


CHAPTER   III. 

THE  IDAHO  BASIN. 

GEOGRAPHICAL  POSITION. 

The  Idaho  Basin  includes  the  headwaters  of  Moore  Creek,  a  tribu- 
tary of  the  Boise  River,  and  is  located  at  a  distance  of  25  miles  in  a 
northwesterly  direction  from  the  city  of  Boise,  at  about  latitude 
43°  50'  and  longitude  115°  50'.  In  comparision  to  its  size  this  dis- 
trict has  produced  a  very  large  amount  of  gold,  chiefly  from  placer 
mines,  but  also  considerable  from  quartz  mines.  The  area  embraced 
in  the  Idaho  Basin — that  is  to  say,  the  productive  part  of  the  same — 
does  not  exceed  150  square  miles.  Its  length  from  north  to  south  is 
15  miles  and  its  maximum  width  about  13  miles. 

DISCOVERY  AND   HISTORY. 

The  placer  mines  of  the  Idaho  Basin  were  discovered  in  August, 
1862,  by  a  party  of  prospectors  from  Walla  Walla.  During  the  fall 
of  the  same  year  the  party  is  said  to  have  been  attacked  by  Indians, 
and  its  leader,  Grimes,  killed  at  Grimes  Pass.  The  party,  after 
ascertaining  the  richness  of  the  placer  deposits,  returned  to  Walla 
Walla  and  formed  a  new  expedition  of  52  men ;  this  party  reached 
the  basin  the  same  year.  The  prospectors  located  first  at  the  pres- 
ent site  of  Pioneerville.  Subsequently  the  gold  gravels  of  Centerville 
were  located,  and  in  December  of  the  same  year  the  rich  diggings  at 
Idaho  City  and  on  Granite  Creek  were  found.  Rapidly  following 
these  discoveries  came  explorations  of  other  mineral-bearing  parts  of 
Idaho.  In  1863  Rocky  Bar  and  the  rich  mines  of  Owyhee  were  found. 
The  influx  of  miners  was  extremely  rapid  after  the  report  of  the  first 
discoveries  had  spread,  and  one  year  after  the  discovery  several  thou- 
sand placer  miners  were  operating  in  the  region.  From  1862  to  the 
present  date  placer  mining  has  been  carried  on  continuously,  the 
operation  being  limited  only  by  the  amount  of  water  available.  Nat- 
urally, however,  the  output  has  gradually  decreased  since  the  first 
years  following  the  discovery,  when,  as  usual  in  placer  regions,  the 
maximum  production  was  reached. 

At  an  early  date  quartz  mines  began  to  be  exploited,  as  it  was  soon 
seen  that  the  placer  deposits  led  up  to  the  decomposed  croppings  of 
numerous  quartz  veins.  At  that  time,  however,  quartz  mining  was 
in  its  infancy,  and  the  ores  could  not  always  bear  the  cost  of  the  treat- 
ment, increased  in  this  case  by  the  long  distance  over  which  machinery 
had  to  be  transported  and  the  high  wages  demanded  for  labor.  At 
the  present  time  there  is  a  considerable  quantity  of  gravel  still  left 
for  exploitation,  but  these  deposits  will  in  time  be  exhausted,  and  the 
gold  production  will  then  have  to  depend  on  the  quartz  mines.  In 
1867  and  1868  at  least  ten  mills  are  reported  to  have  been  in  operation. 

651 


652 


IDAHO   MINING   DISTRICTS. 


During  the  last  year  only  a  few  of  the  quartz  mines  and  mills  were 
running. 

At  the  present  time  the  Idaho  Basin  contains  five  towns,  with  an 
aggregate  of  1,200  inhabitants.  Idaho  City  is  located  on  Moore  Creek, 
Centerville  and  Pioneerville  on  Grimes  Creek,  and  Placerville  and 
Quartzburg  on  the  different  branches  of  Granite  Creek. 

PRODUCTION. 

The  total  gold  production  of  the  basin  since  its  discovery  has  been 
the  subject  of  frequent  discussion,  and  it  may  be  said  that  it  is 
impossible  to  obtain  undisputed  data.  It  is  often  stated  that  the  pro- 
duction for  the  first  six  years  amounted  to  over  $40,000,000,  and  that 
the  total  production  exceeds  $100,000,000.  As  will  be  shown,  this 
estimate  must  be  regarded  as  extravagant.  The  following  table  shows 
the  production  of  the  State  of  Idaho  according  to  the  most  reliable 
estimates,  contained  in  the  reports  of  J.  Ross  Browne  and  R.  W. 
Raymond,  and  the  later  Mint  reports : 

Production  of  gold  and  silver  in  Idaho,  1863-1876. ' 


Year. 

Value. 

Remarks. 

1863.     ... 

$7,  000,  000 

Estimate  (W.  L.).    Reports  lack- 

1864   

6,  470,  100 

ing. 
J.  Boss  Browne,  report  1867,  based 

1865 

6,581,400 

on  Wells-Fargo  data;  estimates 
added. 
Do. 

1866  
1867  
1868  
1869...... 
1970  
1871  

8,  023,  700 
6,  500,  000 
7,  000,  000 
7,  000,  000 
6,  000,  000 
5,  000,  000 

Do.2 
Mint  reports. 
Do. 
Do. 
Do. 
Do. 

1872  
1873 

2,  695,  900 
2,  500,  000 

$2,300,000  gold,  $400,000  silver. 
From  Eleventh  Census,  Mineral 

1874  

1,880,000 

Industries,  p.  40. 
Do. 

1875 

1,750,000 

From  Eleventh.  Census,  Mineral 

1876. 

1,600,000 

Industries,  p.  40.     $1,554,902  in 
Mint  reports. 
Reports  lacking.       Estimate    by 

W.  L. 

Total. 

70,001,100 

1  During  these  years  the  defective  statistics  do  not  permit  the  separation  of  the  gold  and  sil- 
ver production,  but  the  latter  is  relatively  small,  as  shown  by  the  figures  for  1872.    Few  silver 
mines  were  worked  up  to  1876. 

2  $17,000,000  in  table  on  p.  40  of  Mineral  Industries,  Eleventh  Census.    Authority  for  this  doubt- 
ful statement  unknown. 


LINDGKEN.] 


GOLD   PRODUCTION    OF   IDAHO. 

Production  of  gold  in  Idaho,  1877-1896. 


653 


Year. 

Value. 

Remarks. 

1877 

$1,500,000 

From  table  in  Eleventh  Census 

1878  

1,  150,  000 

Mineral  Industries,  p.  41. 
Do. 

1879       . 

1,  200,  000 

Do. 

1880 

1,980,000 

Do. 

1881  

1,700,000 

Do. 

1882 

1,500,000 

Do. 

1883  

1,400,000 

Mint  reports. 

1884 

1,250,000 

Do. 

1885     . 

1,837,400 

Do. 

1886  

1,798,000 

Do. 

1887.  
1888  
1889 

2,  417,  300 
1,960,000 
2,  055,  700 

Mint  reports;  $1,900,000  accord- 
ing to  Eleventh  Census  table. 
Mint  reports;    $2,400,000  accord- 
ing to  Eleventh  Census  table. 
Mint  reports. 

1890.  

1,696,700 

Do. 

1891  
1892  

1,  685,  600 

1,721,400 

Do. 
Do. 

1893 

1,693,600 

Do. 

1894     . 

2,  308,  800 

Do. 

1895  
1896 

2,594,700 
2,  323,  700 

Do. 
Do. 

Total- 

35,  772,  900 

9 

It  appears  from  the  tables  that  the  total  production  of  the  State  for 
the  first  six  years  scarcely  exceeded.  $41,000,000,  according  to  the  Mint 
statistics,  and  that  consequently  the  Idaho  Basin  can  not  have  pro- 
duced more  than  a  fraction  of  this  amount.  Even  admitting  the  more 
liberal  estimates  mentioned  a  few  lines  below,  the  total  production  for 
this  period  can  not  have  exceeded  $60,000,000.  As  to  the  production 
of  the  Idaho  Basin  itself,  the  data  available  are  still  more  imperfect. 
For  1867,  1868,  and  1870  there  is  in  Raymond's  reports  for  1869  and 
and  1871  an  estimation  of  the  total  production  made  by  W.  A.  Atlee, 
agent  of  the  Wells-Fargo  Company  at  Boise,  an  authority  probably 
better  qualified  to  judge  than  anybody  else.  This  includes  not  only 
Wells-Fargo  shipments,  but  estimates  of  all  kinds  of  shipments. 


654  IDAHO    MINING    DISTRICTS. 

Estimation  of  the  total  production  of  the  Idaho  Basin  in  1867,  1868,  and  1870. 


District. 

1867. 

1868. 

1870. 

Placerville                   

$363,  237 

$340,  515 

$184,  428 

Centerville 

468,  556 

442,  443 

249,  839 

Pioneerville        

494,  931 

552,  604 

250,  000 

Idaho  City            .  -             

3,001,568 

2,961,213 

2,  000,  584 

Total  

4,  328,  292 

4,  296,  775 

2,  684,  851 

The  same  authority  estimates  a  total  production  in  Idaho  of  $9,000, 

000  in  1867,  $10,000,000  in  1868,  and  $6,000,000  in  1870.     On  this  Mr. 
R.  W.  Raymond  comments  that  his  estimate  for  the  total  production 
in  Idaho  for  1868  is  only  $7,000,000,  and,  admitting  the  excellent  facili- 
ties which  Mr.  Atlee  had  for  estimation,  still  thinks  that  his  values 
are  too  high,  and  is  reluctant  to  allow  any  increase  in  his  own  figures. 
From  1881  to  the  present  year  the  statistics  are  in  better  condition, 
and  the  production  of  Boise  County  can  be  closely  estimated.     In  this 
production  the  Idaho  Basin  furnishes  by  far  the  largest  quantity  of 
gold;  it  may  be  safely  said  that  nine-tenths  of  the  production  of  Boise 
County  is  derived  from  the  Idaho  Basin.     On  the  basis  of  these  data 

1  have  attempted  to  construct  a  table  giving  the  probable  production 
of  the  Idaho  Basin  to  the  present  date.     It  is,  of  course,  only  a  rough 
estimate,  but  it  has  some  value. 

During  1884,  Plowman's  claim,  according  to  the  Mint  reports,  yielded 
$25,000,  Channel's  claim  at  the  head  of  Willow  Creek  $10,000,  and  the 
Granite  Creek  Company's  claim  east  of  Placerville  from  $15,000  to 
$20,000.  The  Chinese  companies  were  during  this  period  estimated 
to  have  produced  $25,000  a  year.  In  1883,  Placerville,  according  to 
the  same  authority,  produced  $25,500,  Idaho  City  $381,500,  and  the 
Deadwood  Basin,  located  in  the  northeast  portion  of  Boise  County, 
$8,000.  It  will  be  noticed  that  the  greatest  production  is  always  that 
of  the  Idaho  City  district. 


LINDGEEN.]  GOLD    PRODUCTION   OF    BOISE    BASIN. 

Table  of  probable  production  of  the  Idaho  Basin,  1863-1896. 


655 


Year. 

Value. 

Remarks. 

1863. 

$3,  000,  000 

Estimated  (W  L  ) 

1864  
1865 

4,  000,  000 
5,  000,  000 

Do. 
Do 

1866  

5,  000,  000 

Do 

1867  

4,  300,  000 

Estimated  by  TV^  A  Atlee 

1868. 

4,  300,  000 

Ross  Browne's  report  for 
Do 

1869. 

1869 

3,  000,  000 

Estimated  (W  L  ) 

1870  
1871  

2,  700,  000 
2,  000,  000 

Estimated  by  W.  A.  Atlee 
mond's  report  for  1871). 
Estimated  (W.L.). 

(Ray- 

1872 

1,000,000 

Do. 

1873. 

800,  000 

Do. 

1874 

700,  000 

Do. 

1875  
1876  . 

600,  000 
600,  000 

Boise  County  (Raymond's 
for  1875). 
Estimated  (W.L.). 

report 

1877  

500,  000 

Do. 

1878. 

500,  000 

Do. 

1879  
1880 

400,  000 
300,  000 

Do. 
Do. 

1881 

300,  000 

Boise  County,  Mint  reports. 

1882.     . 

290,  000 

Do. 

1883  

565/000 

Do. 

1884 

400,  000 

Do. 

1885     . 

619,  000 

Do. 

1886  

390,  900 

Do. 

1887 

502,  200 

Do. 

1888  

283,  000 

Do. 

1889  
1890  • 

274,  600 
320,  400 

Do. 
Do. 

1891  

356,  700 

Do. 

1892 

376.  400 

Do. 

1893  
1894  
1895  
1896.    .. 

280,  800 
32T,  800 
339,  000 
326,  000 

Do. 
Do. 
Do. 
Do. 

Total. 

44,651,800 

It  will  be  seen  from  this  table  that  the  total  production  amounts  to 
less  than  $45,000,000.  Allowing  for  the  uncertainty  in  the  data,  we 
may  safely  say  that  the  basin  has  not  produced  more  than  $50,000,000 


656  IDAHO    MINING   DISTRICTS. 

in  gold.  Even  supposing  the  admittedly  uncertain  production  of  the 
first  four  years  to  be  double  the  amount  of  estimates  here  given,  the 
total  production  would  be  only  $62,000,000. 

While  it  is  not  possible  to  separate  the  production  of  the  quartz 
mines  from  that  of  the  placer  mines,  it  may  be  said  with  some  confi- 
dence that  the  total  production  of  the  former  does  not  exceed 
$4,000,000. 

TOPOGRAPHY. 

The  Idaho  Basin,  the  topography  and  geology  of  which  are  shown 
in  PL  XCVI,  is  located  in  the  middle  of  that  great  irregular  mountain 
mass  extending  between  the  Salmon  and  the  Snake  rivers.  Defined 
more  closely,  it  is  situated  on  the  ridge  between  the  north  fork  of 
the  Boise  River  and  the  south  fork  of  the  Payette.  On  the  west  rises 
the  Boise  Range,  the  summits  of  which  are  visible  from  Boise,  and 
which  attains  elevations  of  from  7,000  to  7,500  feet.  On  the  east  rise 
the  irregular  mountain  complexes  of  Sawtooth  Range  and  its  pro- 
jecting spurs.  The  basin  occupies  the  head  waters  of  Moore  Creek,  a 
tributary  joining  the  Boise  River  10  miles  above  where  it  leaves  its 
canyon  and  enters  the  plains  of  the  Snake  River  Valley.  Ten  miles 
from  its  junction  with  the  Boise  River  Moore  Creek  divides  in  two, 
the  westerly  branch  being  called  Grimes  Creek.  Five  miles  above 
this  the  narrow  canyon  in  which  Moore  Creek  flows  widens  out  to 
a  broad  valley,  in  which  the  creek  meanders  with  but  little  fall.  At 
Idaho  City  the  creek  branches  again,  and  both  forks  head  in  the  high 
mountains  near  Wilson  Peak  and  Elk  Creek  Mountain.  A  long  ridge 
with  a  southwesterly  direction  separates  the  Moore  Creek  Basin  from 
the  depression  of  Grimes  Creek.  This  ridge,  which  for  a  long  distance 
has  a  nearly  level  summit,  rises  to  a  height  of  1,000  feet  above  Idaho 
City.  To  the  south  and  east  of  Idaho  City  the  rise  is  much  more 
rapid.  From  the  vicinity  of  Thorn  Creek  Mountain  a  number  of  very 
high  and  narrow  ridges  project  northward,  encircling  the  southern 
and  eastern  part  by  a  chain  of  hills  rising  2,000  feet  above  Idaho 
City.  Six  miles  above  Idaho  City,  Moore  Creek  enters  this  rugged 
complex  of  mountains,  and  5  miles  farther  up  heads  in  the  precip- 
itous amphitheaters  of  Elk  Creek  Mountain. 

The  canyon  of  Grimes  Creek  reaches  to  a  point  10  miles  above  its 
junction  with  Moore  Creek;  then  the  valley  broadens,  exactly  simi- 
larly to  the  valley  of  Moore  Creek,  the  main  branch  continuing  in  a 
northeasterly  direction  and  heading  near  Grimes  Pass,  4  miles  north  of 
Pioneerville.  This,  pass  forms  the  water-parting  between  the  Payette 
and  Boise  rivers.  It  is  comparatively  low,  attaining  an  elevation 
of  only  5,000  feet.  Immediately  east  of  Pionee.rville  and  of  Grimes 
Pass  the  high  ridges  of  Wilson  Peak  and  Summit  Flat  rise  above  the 
more  gently  undulating  country  of  the  valley  of  Grimes  Creek.  An 
important  tributary,  Granite  Creek,  enters  4  miles  below  Centerville 
and  extends  in  a  northwesterly  direction  toward  Quartzburg.  Granite 


LINDQREN.]  TOPOGRAPHY CREEK    GRADES.  657 

Creek  flows  in  a  similar  wide  valley  with  gentle  slopes,  and  passes 
again  lead  over  to  the  Pay ette  watershed  north  of  Place rville  and  north 
of  Quartzburg.  The  lowest  pass  is  the  former,  which  attains  an  eleva- 
tion of  only  4,700  feet.  A  short  distance  west  of  Granite  Creek  the 
Boise  Ridge  rises  very  abruptly  in  the  vicinity  of  Quartzburg,  and 
more  gently  farther  south  to  elevations  ranging  up  to  7,500  feet.  The 
lowest  pass  leading  across  the  Boise  Ridge,  with  an  elevation  of  5,500 
feet,  is  found  6  miles  west  of  Centerville. 

One  can  best  appreciate  the  topographic  features  of  the  basin  when 
standing  high  up  on  the  slopes  of  the  Boise  Ridge  or  on  any  one  of 
the  high  peaks  rising  toward  the  east.  It  is  seen  that  the  name  is 
extremely  appropriate,  because  it  forms  a  low  depression  encircled  on 
all  sides  by  a  ring  of  high  mountains.  Only  toward  the  north,  along 
the  water-parting  between  Boise  Ridge  and  Grimes  Pass,  is  there  a 
lower  rim,  leading  over  into  the  deep  canyon  of  the  Payette  River. 
In  the  accompanying  photograph  (PL  XCI),  taken  from  a  point  at  an 
elevation  of  6,000  feet  on  the  road  leading  from  Quartzburg  to  Jeru- 
salem Valley,  the  encircling  rim  from  Thorn  Creek  Mountain  to  "Wil- 
son Peak  is  well  shown,  as  are  the  remarkably  level  ridges  separating 
the  lowest  depressions  in  the  basin. 

GRADES    OF   THE   WATER    COURSES. 

According  to  the  topographic  maps  of  the  United  States  Geological 
Survey  the  grade  of  the  Boise  River  above  and  below  the  mouth  of 
Moore  Creek  is  very  slight,  being  only  about  10  feet  per  mile. 
Moore  Creek  for  the  first  11  miles  from  its  mouth,  to  the  junction 
with  Grimes,  has  a  grade  of  40  to  50  feet  per  mile.  The  narrow 
canyon  above  the  mouth  of  Grimes  Creek  has  a  somewhat  stronger 
grade,  approximating  66  feet  per  mile.  From  Idaho  City  down  to 
where  the  canyon  begins  a  grade  of  50  feet  per  mile  is  obtained; 
above  Idaho  City  it  is  for  3  miles  33  feet  per  mile;  beyond  this  point 
the  grade  increases  rapidly  and  is  from  100  to  200  feet  per  mile. 

For  the  first  9  miles  from  the  junction  Grimes  Creek  averages  40 
feet  per  mile;  then  follow  4  miles  of  a  more  abrupt  canyon,  with  a 
grade  of  80  feet  per  mile.  Within  the  basins  of  Centerville  and 
Graniteville  the  creeks  have  a  fall  of  about  30  feet  per  mile,  which 
above  Pioneerville  and  Quartzburg  rapidly  increases  to  200  feet  per 
mile. 

TERTIARY  AND  PLEISTOCENE  FORMATIONS. 

• 
LOWER  MOORE   CREEK  VALLEY. 

Configuration  of  the  valley. — From  Boise  River  up  to  the  junction 
with  Grimes  Creek,  Moore  Creek  flows  in  a  somewhat  broad  and 
U-shaped  valley,  the  slopes  of  which  rise  with  increasing  steepness 
to  ridges  with  gentle  summit  lines  2,000  feet  above  the  valley.  The 
hills  are  covered  with  a  scant  vegetation  and  the  soft  crumbling 
18  GEOL,  PT  3 42 


658  IDAHO    MINING    DISTRICTS. 

granite  is  easily  washed  down  by  atmospheric  agencies.  The  width 
of  the  valley  between  the  summits  is  not  more  than  2  miles.  Above 
the  mouth  of  Grimes  Creek  the  valley  contracts  and  the  steep  slopes 
project,  the  creek  forming  a  more  V  shaped  valley,  which  continues 
to  44  miles  above  the  junction.  A  few  small  alluvial  flats  lie  in  the 
bottom  of  this  canyon. 

The  basalt  flow. — The  valley  bottom  is  filled  with  a  basalt  flow  rarely 
over  one-fourth  of  a  mile  in  width ;  its  top  rises  to  about  100  feet  above 
the  creek  level.  Through  this  flow  the  stream  has  cut  down  to  a  depth 
somewhat  exceeding  that  which  it  had  attained  before  the  basaltic 
eruption.  The  joints  in  the  basalt  have  produced  perpendicular 
cliffs,  the  whole  being  an  exact  illustration  of  a  canyon  within  a  valley. 
"While  much  of  the  basalt  flow  has  been  eroded,  enough  remains  to 
form  a  nearly  continuous  fringe  of  cliffs  on  either  or  both  sides  of  the 
streams,  reaching  from  the  mouth  of  the  creek  up  to  1^  miles  above 
the  junction  with  Grimes  Creek.  The  level  top  of  the  flow  has  been 
covered  by  a  sloping,  sandy  wash  from  the  adjoining  hills.  The 
character  of  the  valley,  the  basalt  flow  and  its  covering,  is  well  illus- 
rated  in  PI.  XCII.  Above  the  point  mentioned  the  basalt  suddenly 
ceases,  and  no  more  of  it,  either  in  outcrops  or  in  pebbles,  is  seen 
above.  It  also  extends  a  few  miles  up  on  Grimes  Creek,  and  it  is 
probable  that  the  vent  was  located  at  some  point  in  the  Grimes  Creek 
Canyon,  and  that  the  flow  backed  up  for  some  distance  on  Moore 
Creek.  The  basalt  is  about  contemporaneous  with  the  flows  of  the 
Snake  and  Boise  rivers — geologically  speaking  recent — being  referred 
to  the  late  Neocene  (Pliocene)  period. 

The  present  stream  gravels. — The  bed  occupied  by  the  stream  is 
generally  narrow,  seldom  exceeding  100  feet  in  width.  The  bed  rock 
is  only  rarely  exposed.  The  creek  is  filled  with  coarse  gravel,  largely 
made  up  of  tailings  brought  down  from  the  Idaho  Basin  by  the  winter 
freshets.  The  maximum  depth  of  these  tailings  is  20  feet.  The 
gravels  in  the  present  stream  have  been  and  are  still  extensively 
washed,  mostly  by  Chinese  using  the  ordinary  appliances  for  river 
mining — dams,  Chinese  pumps,  and  derricks.  The  old  channel  cov- 
ered by  the  recent  debris  has  been  exposed  by  mining  at  many  places, 
being  naturally  richer  than  the  tailings.  The  many  basalt  bowlders 
found  in  it  are  a  considerable  obstacle  to  cheap  mining.  On  Moore 
Creek,  about  4£  miles  above  the  mouth  of  Grimes  Creek,  a  steam 
dredge  was  operated  in  1896,  with  the  purpose  of  striking  the  rich 
gravel  10  to  20  feet  below  the  surface.  The  gravel  is  reported  to  have 
been  reached,  though  the  large  bowlders  interfered  somewhat  with 
the  work.  On  the  whole,  the  present  stream  gravels  of  lower  Moore 
Creek  can  not  be  considered  to  have  been  extremely  rich. 

The  gravels  below  the  basalt. — The  basalt  along  Moore  Creek  is 
found  to  rest  on  stream  gravels  accumulated  in  the  bed  before  the 
molten  flow  poured  down  the  valley.  The  old  channel  is  sometimes 


LINDQEEN.]         GRAVELS    OF    LOWER    MOORE    CREEK    VALLEY.  659 

preserved  on  the  east  side  of  the  creek,  sometimes  on  the  west  side, 
which  makes  it  necessary  to  well  establish  the  course  of  the  channel 
before  commencing  extensive  work.  The  old  gravel  is  found  at  ele- 
vations of  from  25  to  75  feet  above  the  creek,  and  has  been  exposed 
by  a  number  of  tunnels.  The  gold  is  fairly  coarse,  the  particles 
being  about  the  size  of  mustard  seeds,  but  it  can  not  be  said  that 
these  old  placers  have  been  shown  to  be  very  rich.  They  have  not 
as  yet  been  extensively  worked.  At  a  place  1  mile  above  Half  Way 
House,  on  the  east  side  of  the  creek,  6  feet  of  granitic  gravel,  covered 
by  3  feet  of  sand,  is  exposed  below  30  feet  of  basalt.  One-half  mile 
farther  up  the  old  channel  is  well  exposed  by  two  tunnels  on  the 
western  side  of  the  creek.  The  old  bed  rock  lies  25  feet  above  the 
stream,  and  the  deposit  has  been  developed  by  175  feet  of  tunnels. 
Above  the  bed  rock  lies  8  feet  of  coarse  gravel  with  a  streak  of  sand 
in  the  middle;  70  feet  of  solid  basalt  covers  this.  The  gravel  is 
reported  to  contain  about  65  cents  per  cubic  yard.  As  the  gravel  is 
not  extremely  compact,  and  as  the  basalt  forms  an  excellent  roof,  it 
might  be  possible  to  profitably  exploit  many  of  these  small  stretches 
of  old  channels  by  underground  hydraulic  operations. 

High  gravels. — Though  the  lower  part  of  Moore  Creek  has  not  been 
thoroughly  examined,  it  has  been  shown  that  gravels  exist  on  some  of 
the  high  ridges  within  this  drainage.  The  study  of  these  high  gravels, 
which  are  probably  of  Tertiary  age,  is  of  the  highest  importance,  as 
it  enables  us  to  trace  more  fully  the  geological  history  of  the  region. 
The  largest  of  these  high  gravels  was  found  on  the  summit  of  a  high 
and  narrow  ridge  between  the  two  forks  of  Thorn  Creek,  at  an  eleva- 
tion of  4,500  feet.  This  deposit,  which  consists  of  extremely  well- 
washed  gravel  of  granitic  and  quartzose  character,  has  been  worked 
to  some  extent  by  the  hydraulic  process  and  found  to  contain  gold  in 
paying  quantities.  The  extent  from  east  to  west  is  only  a  few  hundred 
feet.  The  depth  of  gravel  is  probably  considerable,  although  difficult 
to  estimate  on  account  of  slides  on  the  steep  slopes.  Small  patches  of 
gravel  are  also  reported  to  exist  on  the  neighboring  ridges.  It  is 
probable  that  during  the  highest  stand  of  the  Neocene  lake  which 
occupied  the  whole  lower  basin  of  the  Snake  River  gravel  deposits 
filled  the  upper  parts  of  Moore  Creek  and  the  Boise  River.  The 
occurrence  of  this  high  gravel  will  be  discussed  again  later  in  con- 
nection with  the  geological  history  of  the  Idaho  Basin. 

UPPER  MOORE  CREEK  VALLEY. 

Configuration  of  the  valley. — Five  miles  below  Idaho  City  the  form 
of  the  valley  suddenty  changes.  From  a  level  bottom  the  slopes  rise 
gradually,  numerous  creeks  branch,  and  the  whole  forms  a  broad, 
basin-like  depression.  The  general  character  is  well  shown  in  PL 
XCIII,  looking  southwest  from  Idaho  City.  Three  miles  above  Idaho 
City  a  narrow  canyon  begins  again.  Seen  from  some  elevation,  the 


6 GO  IDAHO    MINING    DISTRICTS. 

three  most  impressive  topographic  features  are  (1)  the  broad  valley; 
(2)  the  level  ridges  between  Idaho  City  and  Centerville,  between  Elk 
Creek  and  Moore  Creek,  and  between  Granite  and  Bannock  gulches, 
rising  to  an  elevation  of  1,000  feet  above  the  valley;  and  (3)  the 
encircling  rim  of  high,  deeply  dissected  peaks  and  ridges,  attaining 
a  height  of  2,000  or  3,000  feet  above  the  valley. 

The  present  stream  gravels. — The  alluvial  gravels  filling  the  bed 
of  the  present  stream  form  broad  flats,  over  which  the  water  course 
meander's  in  changing  channels.  The  largest  part  of  these  gravels  is 
debris  from  the  hydraulic  mining  operations  carried  on  in  the  bench 
gravels  and  the  high  gravels.  The  width  of  the  tailings  below  Idaho 
City  reaches  1,000  feet.  In  two  places  the  channel  contracts  between 
low,  projecting  hills.  At  Idaho  City  the  maximum  width  is  reached; 
here  the  tailings  are  about  2,000  feet  wide,  contracting  again  to  a  nar- 
row channel  1£  miles  above  the  city.  Two  and  one-half  miles  above 
the  same  place  a  comparatively  narrow  canyon  begins,  and  the  tail- 
ings are  only  up  to  200  feet  wide.  The  tailings  cover  the  imperfectly 
washed  original  creek  bed,  and  in  many  places  also  the  first  (lowest) 
terrace  or  bench.  At  Warm  Springs  they  are  reported  to  be  15  feet 
deep;  at  Idaho  City  as  much  as  40  feet.  They  consist  chiefly  of 
granitic  and  porphyritic  pebbles,  with  much  sand.  By  a  natural  proc- 
ess the  gold  in  the  tailings  is  gradually  concentrated.  At  some  time 
the  whole  creek  bed  will  probably  be  washed  over  again  to  recover 
this  gold  and  to  reach  the  older  bottom  gravels,  which  are  supposed 
to  be  rich  in  many  places.  Probably  the  only  way  in  which  this  can 
be  profitably  done  is  by  means  of  hydraulic  elevators  or  dredges. 

The  stream  gravels  were  most  extensively  worked  in  early  days. 
Moore  Creek  was  very  rich  up  to  the  mouth  of  Gambrinus  Gulch, 
though  gravels  have  been  washed  still  higher  up.  The  gulches  enter- 
ing from  the  south,  as  a  rule,  paid  only  for  a  short  distance  from 
the  main  creek;  their  upper  courses  were  nearly  barren.  On  the 
northern  side,  Gambrinus  and  Illinois  gulches  were  extremely  rich. 
Bear  Gulch  has  also  been  worked  extensively.  The  bottom  of  Elk 
Creek  in  its  upper  course  is  generally  narrow,  but  was  rich  up  to 
Boulder  mine;  2  miles  below  Boulder  mine  the  creek  bottom  widens 
to  200  feet,  and  placer  diggings  were  being  operated  in  1896.  Deer 
Creek,  heading  at  Summit  mine,  yielded  very  heavily,  the  output  of 
the  half  mile  near  the  summit  being  placed  at  $90,000.  Wolf  Creek 
has  been  worked,  but  was  not  so  rich.  Spanish  Creek  was  also 
worked,  and  near  its  head  lies  a  flat,  one-eighth  mile  wide  and  one- 
half  mile  long,  covered  by  12  feet  of  angular  wash,  which  has  been 
extensively  worked,  the  gold  being  probably  derived  from  small 
seams  or  from  a  gold-quartz  vein  not  yet  discovered. 

The  gulches  entering  from  the  north  and  south  below  Idaho  City 
were  generally  barren  beyond  the  extent  of  the  terraces. 

Bench  gravels. — Where  the  broad  valley  opens,  6  miles  below  Idaho 


LINDGKEN.] 


GRAVELS  OF  UPPER  MOORE  CREEK  VALLEY. 


661 


City,  a  series  of  shelf-like  terraces,  entirely  absent  farther  down, 
begin  to  appear.  The  width  is  only  a  few  hundred  feet,  and  rarely 
are  longer  stretches  of  them  preserved,  each  little  creek  and  gully 
usually  cutting  the  terrace  in  two.  For  the  first  4  miles  most  of  the 
gravel  patches  lie  on  the  northern  side  of  the  valley.  At  least  twp 
terraces  may  here  be  recognized,  the  bed  rock  of  the  lower  one  being 
50  and  of  the  upper  about  10O  feet  above  the  creek.  The  depth  of 
the  gravel  is  seldom  over  30  feet,  though  near  the  bed-rock  slopes 
much  debris  has  slid  down  over  the  gravel.  All  of  these  gravel 
patches  have  been  very  rich,  and  work  is  still  in  progress  on  some  of 
them.  The  bed  rock,  as  far  up  as  1  mile  below  Warm  Springs,  is 
granite  or  granite-porphyry. 

Above  Warm  Springs  the  gravel  terraces  or  benches  are  very  pro- 
nounced and  often  form  continuous  streaks  of  considerable  length. 
The  best  exposures  are  found  at  Turner's  claim,  1  mile  below  Idaho 
City,  on  the  road  to  Warm  Springs.  At  this  place  the  gravel  ter- 
races occupy  a  total  width  of  one-half  mile,  and  rest  partly  on  gran- 


Moore  Creek 
TatfJngs 


Horizontal  Sc&te. 

IOOO 


Feel- 


Vei-rlcal  Scale. 

)  IOO  ZOO  300 


feel- 


FIG.  55.— Gravel  benches  1}  miles  below  Idaho  City. 

ite,  partly  on  Tertiary  lake  beds,  gently  inclined  westward.  Fig.  55 
shows  a  profile  of  the  different  terraces  here  exposed.  The  highest 
terrace  is  found  at  an  elevation  of  80  feet  above  the  creek  bed. 
Below  this  there  are  three  others,  and  possibly  four,  at  intervals  of 
15  and  30  feet.  The  lowest  terrace  is  said  to  be  covered  by  the  tail- 
ings. These  gravels  have  been  very  extensively  washed,  but  a  con- 
siderable amount  still  remains.  The  upper  terrace,  illustrated  in 
fig.  56,  is  covered  by  8  to  12  feet  of  well-washed  gravel,  chiefly  gra- 
nitic in  character.  This  contains  the  largest  part  of  the  gold,  and 
rests  on  the  eroded  surface  of  the  soft  lake  beds.  This  pay  gravel 
is  again  covered  by  12  feet  of  fine  sandy  or  clayey  sediments  with 
occasional  carbonaceous  seams.  In  this  there  is  but  little  gold.  On 
top  rests  8  feet  of  angular  surface  gravel,  washed  down  from  the 
adjoining  hillside.  This  gravel  is  barren.  The  gravel  terrace  extends 
in  a  northeasterly  direction  along  Elk  Creek,  and  is  chiefly  developed 
on  the  western  side.  The  continuous  bodies  give  way  to  isolated 
patches,  and  2  miles  above  Idaho  City  Elk  Creek  passes  into  a  nar- 
row canyon.  In  Idaho  City  gravel  terraces  are  noted  surrounding  a 


662 


IDAHO    MINING    DISTK1CTS. 


high  body  of  older  gravel  called  East  Hill.  A  part  of  this  terrace, 
on  which  the  town  stands,  has  not  yet  been  mined.  Opposite  Idaho 
City,  and  in  fact  all  along  the  southern  side  of  Moore  Creek  up  to 
the  mouth  of  Granite  Creek,  the  gravel  benches  are  more  or  less  con- 
tinuous. The  lowest  is  noted  20  feet  above  the  creek  and  higher 
ones  are  at  50  and  100  feet.  Small  benches  occur  on  the  north  side 
of  Moore  Creek  east  of  Idaho  City.  At  least  three  different  benches 
may  be  recognized  at  the  elevations  noted.  Most  of  these  bench 
gravels  near  Idaho  City  rest  on  lake  beds  of  sandy  or  gravelly  char- 
acter, usually  referred  to  by  the  miners  as  ' '  false  bed  rock. " 

All  the  small  patches  of  gravel  terraces  have  been  extensively 
washed  and  are  not  yet  quite  exhausted.  The  thickness  of  the  gravel 
rarely  exceeds  25  feet. 

Above  the  mouth  of  Granite  Creek,  Moore  Creek  enters  a  canyon, 
along  which  there  are  but  small  indications  of  gravel  terraces.  At 
Plowman's  sawmill  the  creek  widens  somewhat,  and  from  here  up 
the  bottom  is  generally  occu- 
pied by  a  flat  100  to  300  feet 
wide,  the  surface  of  which  is 
10  to  20  feet  above  the  creek. 
Upon  the  sides  are  occasional 
benches  at  an  approximate 
height  of  50  feet  above  the 
creek.  All  these  low  terraces 
have  been  washed  as  high  up 
as  the  mouth  of  Gambrinus 
Gulch,  and  from  the  evidence 
of  the  old  washings  it  is  clear  . 

FIG.  56.  — Section  of  highest  bench,  1J  miles  below 

that  most   of  the  gold   came  Idaho  city. 

down  from  this  gulch.    Above 

Gambrinus  Gulch  the  washings  are  less  extensive,  and  some  of  the 
low  gravel  flats  have  never  been  worked,  being  evidently  too  poor. 
Two  miles  above  Idaho  City,  as  stated  above,  Elk  Creek  enters  a  nar- 
row canyon,  and  although  this  widens  somewhat  farther  up,  still 
there  are  only  occasional  patches  of  gravel  terraces  remaining,  at 
elevations  of  about  50  feet  above  the  creek.  The  manner  of  mining 
the  bench  gravels  by  the  hydraulic  process  is  shown  on  PI.  XCIV. 

High  gravels. — There  are  several  bodies  of  gravel  in  the  vicinity  of 
Idaho  City  which  in  their  occurrence  differ  from  the  ordinary  bench 
gravels,  and  which  are  generally  at  high  elevations  above  the  creeks. 
While  these  also  are  probably  former  terraces  of  the  valley  of  Moore 
Creek,  they  are  much  older,  and  it  seems  desirable  to  treat  them 
separately. 

The  slope  opposite  Idaho  City  is  occupied  up  to  400  feet  above  the 
creek  by  soft  lake  beds  cut  up  into  sharp  ridges  separated  by  deep 
and  narrow  ravines.  The  gently  sloping  tops  of  these  ridges  are 


8  r&eh  Angular 
Surface  Gravel. 


LINUGREN.] 


GRAVELS    OF    MOORE    CREEK   VALLEY. 


663 


covered  by  auriferous  gravels  which  have 
a  thickness  of  60  feet  or  less.  The  base 
of  these  gravels  lies,  at  Barker's  claim,  300 
feet  above  Moore  Creek.  This  gravel  shows 
excellent  fluviatile  stratification,  and  appears 
to  rest  in  a  flat  channel  eroded  in  the  lake 
beds.  The  gravel  consists  of  well-washed 
granite  pebbles,  accompanied  by  some  of 
quartz.  Bowlders  2  feet  in  diameter  occur 
occasionally.  This  gravel  is  quite  rich,  the 
best  pay  being  found,  as  usual,  on  the  bed 
rock,  i.  e.,  on  the  soft  lake  beds,  but  there  is 
also  gold  distributed  through  the  gravel. 
The  gravel  and  gold  has  also,  of  course,  slid 
down  the  steep  hillside,  and  this  material 
covering  the  slopes  has  been  washed.  Dur- 
ing the  summer  of  1896  the  claim  of  Mr. 
Barker,  1  mile  southeast  of  Idaho  City,  was 
worked  by  the  hydraulic  process.  The  pay 
gravel  does  not  extend  southward  beyond 
the  lake  beds.  In  these  high  gravels  there 
occur-  somewhat  abundant  large  cobbles  up 
to  1  foot  in  diameter  of  quartz  stained  brown- 
ish, and  which  are  often  rich  in  gold,  one 
bowlder  sometimes  yielding  $20.  The  source 
of  this  quartz  is  not  known.  It  certainly  does 
not  come  from  the  high  hills  to  the  south. 
Fig.  57  shows  the  general  relations  of  the 
high  gravels  at  Idaho  City. 

Another  important  bodj^of  the  high  gravels 
is  found  on  the  hill  immediately  east  of  Idaho 
City.  The  gravel ,  which  reaches  a  total  depth 
of  100  feet,  forms  a  body  about  2,000  feet  long 
and  1,000  feet  wide.  It  rests  throughout  on 
clayey  and  sandy  lake  beds,  dipping  gently 
westward  at  an  angle  of  10°.  Seen  from  the 
south  side  of  the  creek,  the  stratification 
planes  in  the  gravel  appear  to  have  a  decided 
dip  westward,  amounting  to  4°,  or  a  little  less 
than  the  underlying  rocks.  The  gravel  rests 
remarkably  evenly  on  the.  lake  beds,  with 
but  little  sign  of  unconformity.  The  geolog- 
ical section  in  fig.  57  illustrates  the  occur- 
rence, while  PI.  XCV  shows  the  gravel  bank 
and  underlying  lake  bed  in  Plowman's  claim. 
A  marked  fluviatile  stratification  is  often 


^v^- 


1f« 

1*1 


^> 


•a 

? i 

<:  2 

t   « 
$]  -3 


664  IDAHO    MINING   DISTRICTS. 

visible.  The  gravel  is  medium  coarse  and  is  made  up  chiefly  of  gran- 
itic bowlders  with  occasional  pebbles  of  quartz.  By  tracing  this  area 
around,  it  is  found  that  the  bed  rock  rises  gently,  being  at  the 
eastern  end  at  least  200  feet  above  the  creek.  At  the  western  end  the 
exposures  are  not  so  good,  as  tailings  and  bench  gravels  lie  up  against 
the  higher  gravels  and  the  underlying  beds  are  not  here  visible.  The 
gravel  on  East  Hill,  as  this  area  is  called,  has  been  worked  by  the 
hydraulic  process  for  a  number  of  years,  and  the  claim  is  reported 
to  have  produced  from  $10,000  to  $20,000  a  year.  The  largest  part  of 
the  gold  is  found  resting  on  the  soft  bed  rock.  The  upper  part  of  the 
gravel  also  contains  some  gold,  but  probably  not  more  than  about  5 
cents  per  cubic  yard.  The  gold  is  fairly  coarse,  and  has  a  value  of 
$16.50  an  ounce  before  melting.  On  the  surface  of  the  gravel  the  gold 
appears  to  be  more  abundant,  which  is  probably  caused  by  a  gradual 
concentration  by  atmospheric  agencies. 

Another  large  body  of  gravel  is  that  known  as  Gold  Hill  (fig.  57), 
occupying  about  160  acres  and  situated  on  the  point  between  the  creek 
and  Bear  Gulch.  The  top  of  this  gravel  body  is  350  feet  above  Idaho 
City,  and  its  greatest  depth  is  probably  not  less  than  200  feet.  Along 
Elk  Creek  and  Bear  Gulch  the  gravel  rests  on  the  same  soft  lake  beds 
which  crop  out  on  East  Hill.  Toward  the  southwest  tailings  lie  up 
against  it.  On  the  northeast  side,  on  the  other  hand,  the  gravel  rests 
directly  on  granite  bed  rock.  Here  also  the  dip  of  the  gravel  beds  is 
about  4°,  while  that  of  the  lake  beds  is  10°  W.  Good  exposures,  made 
by  hydraulic  mining,  are  seen  on  the  southwest  side.  One-fourth 
mile  north  of  Idaho  City  the  surface  of  the  soft  lake  beds  lies  20  feet 
above  the  creek.  Above  the  lake  beds  lies  15  feet  of  coarse  heavy 
gravel  with  many  subangular  fragments.  Above  this  is  10  feet  of 
sand  with  clay  streaks,  sometimes  a  little  coaly,  and  somewhat 
resembling  the  lake  beds.  Capping  this  sand  is  ordinary  well- washed 
gravel.  Here,  as  in  the  other  gravel  bodies,  the  largest  pay  was 
found  on  the  surface  of  the  bed  rock — that  is,  on  the  surface  of  the 
lake  beds — and  this  rich  bottom  stratum  has  been  mined  by  the  drift- 
ing process  both  on  the  southeast  and  our  the  southwest  side.  A  large 
body  of  gravel  here  remains,  which  can  be  worked  by  the  hydraulic 
process,  although  it  is  probably  of  low  grade.  Owing  to  some  diffi- 
culty in  procuring  water,  the  claims  on  this  hill  have  not  yet  been 
extensively  worked. 

On  the  ridges  above  these  deposits  no  other  gravel  masses  have  been 
found,  but  a  small  body  rests  on  a  sidehill  to  the  east  of  Elk  Creek,  3 
miles  northeast  of  Idaho  City,  at  an  elevation  of  about  200  feet  above 
the  creek.  On  the  western  side  of  Elk  Creek,  opposite  Idaho  City, 
small  patches  of  gravel  are  occasionally  found  200  feet  above  the 
creek  level,  and  scattered  pebbles  occur  in  many  places  at  about  this 
elevation.  Still  another  body  of  high  gravel  is  that  found  on  the 
point  between  Granite  Creek  and  Moore  Creek,  east  of  Idaho  City. 


L1NDGKEM.] 


LAKE    BEDS    OF    MOORE    CREEK    VALLEY. 


665 


It  forms  a  bench-like  deposit  175  feet  above  the  creek,  and  the  larger 
part  of  it  has  been  worked  by  the  hydraulic  process. 

Lake  beds. — Near  Idaho  City,  on  both  sides  of  Moore  Creek,  a  con- 
siderable area  is  covered  by  soft  sedimentary  beds  of  clay,  sand,  and 
gravel.  These  do  not  bear  evidence  of  being  river  deposits.  The 
regular  stratification  and  their  general  character  indicate  that  they 
have  been  deposited  in  a  body  of  water,  in  all  probability  a  fresh- 
water lake.  These  beds  do  not  contain  any  notable  amount  of  gold, 
but  the  fluviatile  auriferous  gravels  just  described  are  deposited  on 
their  eroded  surface.  The  dip  of  the  beds  proves  that  that  they  have 
been  disturbed  since  their  deposition.  Recognizing  their  sedimentary 
nature,  the  miners  call  these  lake  beds  "false  bed  rock."  The  lake 
beds  are  first  met  with  1  mile  below  Warm  Springs,  where  they  appear 
as  semiconsolidated  white  sand  and  clays.  Near  Warm  Springs  they 
assume  the  form  of  coarse  yellowish  sandstones,  evidently  cemented 
by  the  opaline  silica  of  the  hot  waters.  In  fact,  sandstone  cemented 

Auriferovs  Gravel  pa rHy  washed  off 


FIG.  58.— Exposure  of  lake  beds  and  auriferous  gravel  1J-  miles  south  of  Idaho  City.    Top  of 
gravel,  400  feet  above  Idaho  City. 

by  fire  opal  has  been  collected  on  both  sides  of  the  creek,  and  the 
occurrence  is  mentioned  by  Mr.  S.  F.  Emmons.1  Owing  to  the  very 
coarse  character  and  rapid  accumulation  of  the  debris  the  stratifica- 
tion is  poorly  preserved.  Half  a  mile  below  the  hot  springs  these  sand- 
stories  form  a  bluff  300  feet  high,  and  also  extend  east  of  the  road, 
producing  a  relatively  narrow  passage  for  the  creek.  A  slide  has 
taken  place  near  the  creek,  covering  an  older  channel,  the  bed  rock  of 
which  lies  only  a  few  feet  above  the  present  creek  and  which  has 
been  mined  by  several  tunnels.  At  Turner's  claim  the  lake  beds  form 
the  bed  rock  and  are  well  exposed.  They  dip  5°  NW.  and  consist  of 
soft  sand  and  clay  with  occasional  coaly  layers.  The  clay  encloses 
nodules  of  iron  pyrite  containing  some  gold  and  silver. 

Near  Turner's  claim  a  projecting  spur  of  granite  reaches  to  within 
a  few  hundred  feet  of  the  road,  and  in  the  hydraulic  cuts  the  lake 
beds  are  seen  to  rest  on  it.  Between  Turner's  claim  and  the  citv  the 


1  Boise  Statesman,  March  29, 1896. 


666  IDAHO    MINING    DISTRICTS. 

lake  beds  are  not  exposed,  but  the  gravel  of  the  terraces  is  reported 
to  rest  on  them.  Across  Elk  Creek  from  Gold  Hill  sandy  and  clayey 
lake  beds  again  appear,  the  bench  gravels  resting  on  their  eroded 
surface.  Granite  appears  a  short  distance  up  on  the  hillside. 

Around  East  Hill  and  Gold  Hill  the  lake  beds  are  well  exposed,  and 
consist  largely  of  greenish  or  gray  clay  with  arenaceous  streaks  and 
intercalated  beds  of  black  clay  with  coaly  streaks.  The  dip  is  10°  W. 
A  few  fossil  plants  were  found  here,  which  were  identified  by  Mr. 
Knowlton.  (See  Appendix,  p.  721.) 

These  plants  identify  the  lake  beds  with  the  Payette  formation  of 
the  foothills,  a  correlation  which  the  field  work  had  shown  to  be  very 
probable.  Considerable  masses  of  fossil  wood  are  reported  to  have 
been  found  in  the  lake  beds  at  the  mouth  of  Steamboat  Gulch,  1  mile 
southeast  of  Idaho  City. 

The  lake  beds  attain  their  greatest  development  south  of  Idaho  City, 
where  they  are  more  than  300  feet  thick.  Their  character  is  here 
prevailingly  sandy,  with  some  medium-coarse  gravels  and  with  occa- 
sional coaly  and  clayey  layers.  The  exposure  illustrated  in  fig.  58 


FJO.  59.— Bench  gravel  and  lake  beds  at  mouth  of  Granite  Creek,  2  miles  west  of  Idaho  City. 

indicates  an  apparent  unconformity  in  the  lake  beds.  They  continue 
up  the  creek,  decreasing  in  width,  to  the  mouth  of  Granite  Creek. 
Good  exposures  are  seen  at  Brockhausen  and  Spiro's  claim,  between 
Granite  and  Bannock  creeks,  where  the  bench  gravels  rest  on  them. 
Fine  gravels  here  appear  in  the  lake  beds,  interstratified  with  clay  and 
sand.  At  the  little  bench  just  south  of  the  mouth  of  Granite  Creek, 
12  feet  of  lake  beds,  dipping  4°  W.,  at  first  gravelly,  then  sandy,  rest 
on  granite,  and  on  the  eroded  surface  of  the  lake  beds  rests  a  patch 
of  bench  gravel  50  feet  above  the  main  creek.  A  few  quartz  pebbles 
are  present  in  the  gravel  of  the  lake  beds  (fig.  59). 

A  small  area  of  clayey  lake  beds  is  said  to  exist  on  the  high  plateau 
several  hundred  feet  above  Moore  Creek  and  about  2  miles  east- 
southeast  of  the  mouth  of  Granite  Creek. 

The  contacts  of  the  lake  beds  with  the  granite  offer  points  of  great 
interest.  It  has  already  been  noted  that  lake  beds  rest  on  granite 
near  Turner's  claim,  at  the  east  end  of  Gold  Hill,  and  at  the  mouth  of 
Granite  Creek.  Everything  indicates  that  they  were  laid  down  on  an 
uneven  surface,  and  probably  in  a  valley  with  configuration  similar 
to  that  of  the  present  Moore  Creek  Basin.  But  at  many  other  places 


LAKE  BEDS  OF  MOORE  CREEK  VALLEY.         607 

it  is  clear  that  the  lake  beds  are  separated  from  the  granite  by 
normal  faults.  One  mile  below  Warm  Springs,  on  both  sides  of 
Moore  Creek,  there  is  evidence  that  the  lake  beds  abut  directly 
against  the  granite.  The  same  relation  is  noted  at  the  sandstone 
bluff,  300  feet  high,  back  of  Warm  Springs.  Here  the  almost  hori- 
zontal lake  beds  abut  against  a  steep  granite  bluff,  and  a  little  lateral 
valley  has  formed  along  the  contact.  There  can  hardly  be  any  doubt 
that  this  steep  bluff  represents  a  fault-scarp.  The  deeply  incised 
gulch  just  southward  gives  similar  testimony  as  to  the  sharp  abut- 
ment of  the  two  formations  against  each  other. 

A  small  hot  spring  is  located  at  a  point  on  this  fault,  and  the  large 
warm  springs  probably  also  issue  from  this  fault,  though  at  present 
they  break  out  through  the  sandstone  a  little  below  it.  The  water 
has  a  very  high  temperature,  and  the  total  quantity  is  probably  not 
less  than  100  miner's  inches.  The  water  is  not  rich  in  dissolved  salts, 
but  has  a  slight  smell  of  sulphureted  hydrogen.  Mr.  J.  B.  Hastings  * 
thinks  that  this  fault  and  the  accompanying  slipping  down  of  this 
mass  of  conglomerate  or  sandstone  caused  the  damming  of  a  lake  and 
the  deposition  of  the  lake  beds.  This  can  not  be  accepted  as  a  cor- 
rect explanation,  for  the  sandstone  is  of  the  same  age  as  the  lake 
beds,  the  deposition  of  which  was  caused  by  events  much  farther 
reaching  than  a  landslide. 

All  along  the  southern  contact  line  of  lake  beds  and  granite,  from 
Moore  Creek  below  Warm  Springs  to  beyond  Bannock  Creek,  the 
evidence  of  a  fault  is  very  decided.  Nearly  everywhere  along  this 
line  the  lake  beds  cease  suddenly,  and  south  of  them  the  granite  rises 
in  a  steep  bluff,  contrasting  strongly  with  the  confused  topography  of 
the  soft  and  sliding  lake  beds.  The  best  evidence  is  found  at  the 
contact  back  of  Barker's  claim,  where  the  contact  plane  between 
granite  and  lake  beds  is  found  to  dip  at  an  angle  of  45°  N.  A  similar 
and  extremely  well-exposed  fault  is  shown  on  both  sides  of  Elk  Creek 
at  the  northern  end  of  Gold  Hill  at  the  mouth  of  Lincoln  Gulch. 

In  conclusion,  the  lake  beds  of  the  Payette  formation  in  the  Moore 
Creek  basin  form  an  area  of  about  7  square  miles;  they  dip  west  or 
northwest  at  angles  of  from  4°  to  14°,  and  they  are  often  separated  from 
the  granite  by  marginal  faults.  They  are  probably  a  remnant  of  a 
more  extensive  area  preserved  by  reason  of  being  sunk  in  the  granite 
by  movement  along  these  faults. 

A  total  thickness  of  from  300  to  400  feet  is  exposed  above  Moore 
Creek.  The  idea  that  rich  gold  gravel  would  be  found  below  the  lake 
beds  led  in  1894  to  the  sinking  of  a  shaft  and  bore  hole  at  Idaho  City, 
only  about  20  feet  above  the  level  of  Moore  Creek.  One  hundred  feet 
of  shaft  were  sunk,  and  then,  when  the  water  became  too  difficult  to 
handle,  a  bore  hole  continued  down  to  a  total  depth  of  516  feet.  It  is 

reported  that  granitic  bed  rock  was  struck  at  that  depth.     Samples 

; 

1  Eng.  and  Min.  Jour.,  July  21, 1894 


668  IDAHO    MINING    DISTRICTS. 

of  boring  show  mainly  granitic  sand  and  clay,  with  nodules  of  iron 
pyrite  occurring  at  frequent  intervals.  The  total  thickness  of  the 
lake  beds  would,  then,  be  not  less  than  850  feet.  A  few  miners'-inches 
of  saline  water  flowed  from  the  well,  as  might  indeed  be  expected,  for 
the  geological  conditions  are  such  that  a  typical  artesian  basin  is 
formed. 

Gold  in  tine  lake  beds. — It  is  stated  that  no  gold  is  contained  in  the 
lake  beds  or  the  false  bed  rock.  This  certainly  seems,  at  first  glance, 
to  be  a  strange  state  of  affairs,  considering  that  the  sands,  clays, 
and  gravels  of  the  lake  beds  consist  of  practically  the  same  material 
as  the  auriferous  gravels.  It  would  seem,  to  imply^  that  the  quartz 
veins  from  which  the  gold  was  derived  were  formed  between  the  period 
of  the  lake  beds  and  that  of  the  gravels.  It  will  be  shown,  however, 
that  the  lake  beds  are  not  entirely  void  of  gold.  Those  just  south  of 
the  mouth  of  Granite  Creek,  shown  in  fig.  59,  were  prospected  with  the 
pan.  In  the  lowest  bed,  consisting  of  coarse  gravel  with  much  sand, 
nothing  was  found;  but  6  feet  above  the  granite,  in  a  finer  gravel 
admixed  with  some  quartz  pebbles,  several  colors  were  found  in  every 
pan.  The  gold  is  extremely  fine  and  of  a  rather  pale  color.  There  is 
very  little  black  sand  in  this  gravel,  but  a  considerable  quantity  of 
monazite.  The  samples  were  taken  under  conditions  that  made  it 
impossible  for  any  of  this  gold  to  have  been  derived  from  the  rich 
gravel  above.  Mr.  Brockhausen  informed  me  that  in  a  claim  one-half 
mile  below  the  mouth  of  Granite  Creek  a  considerable  amount  of  gold 
was  taken  out  of  a  bed  of  gravel  dipping  below  the  false  bed  rock. 

At  the  mouth  of  Noble  Gulch,  opposite  Idaho  City,  there  is  a  bed 
of  gravel  a  few  feet  thick  dipping  below  strata  of  carbonaceous  clay. 
This  gravel  has  been  worked  and  is  reported  to  have  yielded  some 
gold.  Mr.  Barker  informs  me  that  a  little  gold  may  occur  in  the 
gravels  of  the  lake  beds  wherever  quartz  pebbles  are  present.  Mr. 
Kramer,  who  owns  a  claim  one-half  mile  below  Warm  Springs,  states 
that  John  Wood,  former  owner  of  the  claim,  obtained  good  prospects 
in  a  bed  of  gravel  dipping  under  the  false  bed  re  •  k  at  that  place.  The 
locality  is  now  covered  up.  Mr.  Turner  states  that  nodules  of  pyrite, 
containing  a  few  dollars  in  gold  and  silver,  are  often  found  in  the 
false  bed  rock.  During  the  sinking  of  the  artesian  well  at  Idaho  City 
certain  strata  were  found  to  contain  much  iron  pyrite,  which  upon 
being  washed  out  and  assayed  was  found  to  carry  as  much  as  $12  per 
ton  in  gold  and  silver. 

It  is  conceded,  however,  that  these  occurrences  of  pyrite  do  not 
necessarily  indicate  an  original  content  of  gold  in  the  lake  beds,  as 
the  precious  metals  may  have  been  leached  from  the  overlying  rich 
gravels  and  deposited  with  the  pyrite  below. 

It  is  thus  certain  that  free  gold  occurs  in  some  of  the  gravel  of  the 
lake  beds.  That  there  could  not  be  much  of  it  present  is  clear  from 
the  mode  of  formation  of  the  lake  beds,  for  they  were  deposited  by 


LINDOREX.]  ROCKS    OF    MOORE    CREEK    VALLEY.  6G9 

rapid  accumulation  in  a  body  of  water  affording  no  opportunity  for 
concentration.  Moreover,  the  detritus  was  mostly  derived  from  the 
immediately  surrounding  hills,  which  are  nearly  barren  of  mineral 
veins,  while  the  overlying  gravels  were  transported,  concentrated, 
and  assorted  by  streams  coming  from  the  region  of  auriferous  quartz 
veins.  It  is  probable  that  a  system  of  streams  existed  before  the  lake 
beds  were  laid  down.  It  would  naturally  be  expected  that  many  of 
these  should  carry  gold,  and  it  is  indeed  probable  that  if  the  lake  beds 
were  removed  we  should  find  auriferous  gravels  on  the  bed  rock  along 
these  lines  of  old  stream  courses.  But  it  is  extremely  unlikely  that  a 
random  bore  hole  would  strike  any  of  these  deposits.  They  could  be 
found  only  by  prospecting  along  the  margin  of  the  lake  beds  and  fol- 
lowing down  any  rich  stratum  that  might  be  found.  In  this  case, 
however,  the  cost  and  difficulties  of  mining  would  be  very  great. 

Olivine-basalt  (dolerite). — One  mile  above  Idaho  City,  on  the  north 
side  of  Moore  Creek,  there  are  peculiar  outcrops  of  a  black  or  dark- 
green  very  tough  rock,  weathering  in  rounded  outcrops,  which  are 
commonly  referred  to  as  "nigger  heads."  Decomposing,  they  yield 
a  dark-red,  yellow,  or  green  clayey  soil.  Gravel  benches  rest  upon 
this  rock,  which  apparently  forms  an  intercalated  bed  up  to  100  feet 
thick  in  the  lake  beds.  The  sheet  lies  flat  at  the  point  indicated, 
crosses  Moore  Creek  in  a  narrow  strait  2  miles  above  the  city,  and 
then,  probably  being  tilted,  rises  to  elevations  of  400  feet  above  the 
creek  near  Pine  Gulch.  Here  it  is  evidently  separated  by  a  fault 
from  the  granite.  The  same  rock  is  found  again  in  nearly  every  one 
of  the  small  gulches  entering  Moore  Creek  opposite  Idaho  City,  and 
here  it  is  covered  by  a  considerable  thickness  of  lake  beds  and  is 
exposed  only  in  the  bottom.  It  is  a  medium-grained,  dark-green 
rock,  with  abundant  scattered  crystals  of  greenish-yellow  olivine. 
Under  the  microscope  it  is  seen  to  be  a  coarse  olivine-basalt  (dolerite), 
and  to  consist  of  large  phenocrysts  of  olivine  and  small  crystals  of 
magnetite  as  the  earliest  product  of  consolidation.  There  is,  further, 
a  large  amount  of  violet-brown  augite  in  large  anhedral  individuals, 
forming  a  sort  of  base,  in  which  are  embedded  the  irregularly  distrib- 
uted laths  of  a  basic  feldspar  (labradorite).  The  olivine  decomposes 
to  brownish-red  products,  also  to  serpentine;  the  augite  to  chlorite, 
with  beautiful  radial  structure.  The  structure  of  the  rock  is  really 
that  of  a  diabase.  This  rock  was  evidently  poured  out  on  the  surface 
as  a  lava  at  the  time  of  deposition  of  the  lake  beds. 

THE  VALLEY  OF  GRIMES  CREEK. 

Configuration. — Four  miles  below  Centerville  the  canyon  widens  to 
a  broad  valley  with  gentle  slopes,  similar  to  that  of  Moore  Creek, 
extending  in  an  east-northeasterly  direction  for  11  miles.  Above  this 
Grimes  Creek  makes  a  sudden  bend,  and,  separated  only  by  a  low 
ridge  from  the  deep  canyon  of  the  Payette  River,  finally  reaches  its 


670  IDAHO    MINING   DISTRICTS. 

headwaters  at  Summit  Flat.  Only  two  tributaries  join  it — Clear 
Creek,  heading  in  the  rugged  mountains  near  Wilson  Peak,  and 
Muddy  Creek,  heading  a  few  miles  northwest  of  Pioneerville. 

Present  stream  gravels. — A  large  amount  of  tailings  lies  nearly  all 
along  Grimes  Creek.  At  Centerville  they  are  900  feet  wide ;  farther 
up  they  narrow  considerably,  where  the  hills  approach  closer  to  the 
creek,  to  widen  again  near  Pioneerville;  above  this  place  the  creek 
enters  a  rather  narrow  canyon.  A  great  mass  of  tailings  also  lies  in 
Muddy  Creek.  Clear  Creek  has  never  been  washed,  and  the  original 
wide  alluvial  grassy  flats  are  here  preserved  in  the  lower  course  of 
the  creek.  Concerning  the  gold  content  of  these  tailings,  the  same 
remarks  apply  here  which  were  made  in  relation  to  those  of  Moore 
Creek.  They  can  doubtless  be  worked  profitably  in  many  places  by 
means  of  hydraulic  elevators  or  dredges.  The  difficulty  is  to  obtain 
a  sufficient  water  supply.  The  beds  of  Grimes  Creek  and  Muddy  Creek 
are  reported  to  have  been  rich  throughout,  while  Clear  Creek  did  not 
pay  well.  Only  a  few  of  the  side  gulches  contained  gold  in  paying 
quantities.  Willow  Creek  was  rich,  and  contained  near  its  head  a  body 
of  angular  gravel,  known  as  Channel's  claim,  which  has  yielded  much 
gold.  Henry  Creek,  leading  up  to  Summit  mine,  was  also  rich.  The 
bulk  of  the  gold  appears  to  have  come  down  from  the  headwaters  of 
Grimes  and  Muddy  Creeks. 

The  tailings  are  very  sandy,  being  composed  of  almost  60  per  cent 
sand  and  40  per  cent  cobbles,  and  the  maximum  depth  is  15  to  20  feet. 
The  lower  part  of  the  tailings  and  benches  of  Grimes  Creek,  up  to  3 
miles  below  Centerville,  is  owned  by  the  Grimes  Creek  Bed  Rock 
Flume  Company ;  the  upper  part,  as  far  as  several  miles  above  Pio- 
neerville, by  the  Wilson  Company,  which  for  many  years  has  carried 
on  active  operations  near  Pioneerville.  The  creek  has  been  worked 
as  far  up  as  the  big  bend  at  Grimes  Pass,  where  the  gravel  is  charac- 
terized by  a  great  many  heavy  bowlders  of  porphyrite.  Many  similar 
cobbles  of  porphyries  also  occur  farther  down  on  Muddy  and  Grimes 
creeks.  Pebbles  of  obsidian  have  been  found  on  Muddy  Creek. 

Bench  gravels. — As  along  Moore  Creek,  gravel  benches  occur  at 
different  elevations  all  along  Grimes  Creek.  The  two  most  prominent 
benches  are  at  elevations  of  30  and  60  feet  above  the  present  creek 
bed,  but  scattered  gravel  occurs  at  higher  elevations  also.  Such  is 
the  thin  gravel  occurring  near  Centerville  up  to  150  feet  above  the 
creek.  These  bench  gravels  have  been  very  extensively  worked,  and 
but  little  remains  of  them  near  Centerville.  A  short  distance  above 
Centerville,  at  a  place  called  Bummer  Hill,  they  were  of  unusual 
richness.  Above  the  narrow  canyon  the  bench  gravels  appear  again 
in  the  open  valley;  where  Muddy,  Clear,  and  Grimes  creeks  join  the 
same  kind  of  benches  are  noted  and  hydraulic  work  has  been  actively 
prosecuted.  Pioneerville  is  situated  on  the  lower  bench,  25  feet 
above  the  creek.  A  low  bench  gravel,  one-half  mile  above  town, 


LINUGUEN.] 


DEPOSITS    IN    GRIMES    CREEK    VALLEY. 


671 


!    Sand  and  Gravel 


Fine  Gravel 


worked  in  1896,  is  illustrated  in  fig.  60.  The  bed  rock  is  at  the  creek 
level,  and  the  work  was  done  by  means  of  hydraulic  elevators,  which 
have  been  extensively  utilized  by  this  company.  The  gold,  which  is 
generally  of  the  size  of  mustard  seeds,  lies  often  on  the  higher  bed 
rock  instead  of  in  the  potholes.  The  lower  gravel  carries  all  the  gold. 

Older  gravels. — The  low  terrace  'separating  Muddy  and  Grimes 
creeks,  one-fourth  mile  northwest  of  Pioneerville,  and  covered  by 
later  bench  gravels,  is  partly  made  up  of  granite,  partly  of  an  older, 
somewhat  cemented,  granitic  gravel.  This  belt  is  only  about  one- 
fourth  mile  wide,  and  the  gravel  abuts  against  the  granite  on  the 
northern  side,  showing  that  it  is  separated  from  it  by  a  fault.  It  is 
evidently  an  older  gravel  sunk  down  along  a  fault-line.  On  the 
southern  side  it  apparently  rests  on  granite.  The  same  fault  is  well 
shown  in  the  creek  on  the  eastern  side,  one-fourth  mile  above  the 
town.  It  is  reported  that  a  shaft  100  feet  deep  was  sunk  in  this  gravel 
some  twenty  years  ago,  without  reaching  the  underlying  granite.  The 
gravel  contains  some 
coarse  gold.  The  side 
hill  immediately  east 
of  this  fault  is  wholly 
composed  of  granite, 
but  above,  on  the  nar- 
row ridge  separating 
Grimes  and  Clear 
creeks,  lies  a  body  of 
somewhat  similar 
gravel,  attaining  an 
elevation  of  200  feet 
above  the  creek.  Gran- 
ite bed  rock  is  found  120  feet  above  the  creek,  and  on  it  rests  a 
bed  of  coarse  gravel  containing  some  gold.  Much  of  this  gravel  has 
been  worked  by  the  hydraulic  process. 

Lake  beds. — ~No  extensive  areas  of  lake  beds  occur  in  this  vicinity, 
but  in  the  valley  of  Muddy  Creek,  2  miles  north  of  Pioneerville,  a 
small  patch  of  a  rather  remarkable  deposit  is  found.  For  a  distance 
of  a  mile  the  creek  runs  in  a  narrow  canyon,  which  then  opens  to  a 
somewhat  wider  valley.  Here  lie,  chiefly  along  the  western  side  of 
the  creek,  beds  of  soft  white  sands,  gravels,  and  clays,  with  a  little 
lignite.  In  one  place  where  the  stratification  could  be  made  out  the 
layers  seemed  to  dip  20°  W.  This  small  mass  of  sedimentary  deposit 
has  a  lacustrine  character,  and  should  probably  be  correlated  with  the 
lake  beds  of  Idaho  City;  it  does  not  contain  any  gold,  but  the  surface 
gravels  resting  on  it  are  said  to  have  been  unusually  rich,  the  softer 
beds  having  acted  as  riffles,  catching  the  gold.  On  all  sides  the 
granite  rises  rather  steeply.  At  Bummer  Hill,  one-half  mile  above 
Centerville,  a  granitic  sand,  which  may  possibly  also  belong  to  this 
lacustrine  series,  forms  the  bed  rock. 


FIG.  60. — Bank  of  bench  gravels  one-fourth  mile  north  of  Pio- 
neerville, level  of  Grimes  Creek. 


672  IDAHO    MINING    DISTRICTS. 

Volcanic  rocks. — A  small  dike  of  andesite  occurs  a  short  distance 
west  of  Grimes  Pass,  and  fragments  of  obsidian  have  been  found  in 
Muddy  Creek. 

THE  VALLEY  OF  GRANITE  CREEK. 

Configuration. — Granite  Creek,  joining  Grimes  Creek  3  miles  below 
Centerville,  extends  from  this  point  in  a  north-northwesterly  direction 
for  a  distance  of  8  miles,  heading  at  the  low  pass  north  of  Quartz- 
burg.  A  number  of  tributaries  join  it  from  east  and  west,  produc- 
ing, in  the  middle  course  of  the  creek,  a  large,  basin-like  depression. 
North  of  Granite  a  narrow  canyon  begins.  Ophir  Creek,  Boyles 
Gulch,  and  Wolf  Creek  head  at  the  relatively  low  divide  toward  the 
Payette  drainage,  while  Fall  Creek,  Trail  Creek,  and  Canyon  Creek 
head  in  the  Boise  Ridge  and  carry  a  great  deal  of  water.  A  broad 
ridge,  only  400  feet  high,  separates  Granite  Creek  and  Grimes  Creek. 

Present  stream  gravels. — As  in  the  districts  already  described,  the 
larger  part  of  the  present  stream  gravels  consists  of  tailings.  They 
are  one-fourth  mile  wide  at  the  junction  with  Grimes  Creek,  but  only 
a  few  hundred  feet  in  width  from  that  place  to  half  a  mile  below  the 
mouth  of  Ophir  Creek.  Here  they  widen  and  attain  a  maximum 
width  of  1,500  feet.  The  tailings  also  reach  far  up  on  Ophir,  Boyles, 
and  Wolf  creeks,  but  narrow  down  to  100  feet  or  less  a  short  distance 
above  Granite.  Along  the  lower  courses  of  Canyon  Creek,  Trail 
Creek,  and  Clear  Creek,  as  far  as  2  or  3  miles  above  their  mouths,  are 
stream  gravels  and  low  terraces,  attaining  in  some  places  a  width  of 
1,000  feet.  These  creeks  have  yielded  scarcely  any  gold,  and  their 
gravels  and  terraces  show  well  the  character  of  the  river  courses  of 
the  basin  before  the  gold  discoveries.  Clear  Creek  was  entirely  bar- 
ren in  its  upper  course.  A  little  gold  was  found  in  one  or  two  places 
along  the  creek  which  Hawkins  toll  road  follows  from  Star  ranch 
westward.  Canyon  Creek  has  produced  a  little  gold,  and  Fall  Creek 
a  considerable  amount.  The  main  creek  has  been  rich  from  the 
junction  up  to  Quartzburg,  while  no  gold  is  found  above  that  town. 
Ophir,  Boyle,  and  Wolf  creeks  were  very  rich  up  to  their  headwaters. 
The  east  fork  of  Alder  Creek,  which  flows  into  the  Payette  and  heads 
opposite  Wolf  Creek,  has  also  produced  some  placer  gold.  It  appears 
to  be  the  only  creek  on  the  Payette  side  which  is  auriferous.  The 
gulches  running  into  Ophir  Creek  from  the  east  have  produced 
scarcely  anything.  In  fact,  most  of  the  broad  ridge  separating  Grimes 
and  Ophir  creeks  is  singularly  barren.  As  to  the  working  of  the 
tailings  in  Granite  Creek,  the  same  remarks  apply  as  have  been 
made  in  the  case  of  the  other  tailings  mentioned  above. 

Bench  gravels. — Benches  are  found  at  intervals  all  along  Granite 
Creek  as  far  up  as  half  a  mile  above  Granite;  also  for  some  distance 
up  Ophir  Creek,  and  up  Wolf  Creek  as  far  as  Placerville.  There  are 
usually  two  well-pronounced  horizons,  the  bed  rock  of  the  lower  one 


LINDGREN.]  GRAVELS   OF    GRANITE   CREEK.  673 

being  20  to  30  feet  above  the  creeks  and  that  of  the  higher  one  at  an 
elevation  of  50  feet.  Near  Granite  and  Placerville  bowlders  of  por- 
phyritic  rocks  are  abundant.  The  benches  opposite  Granite  also  con- 
tain many  basaltic  bowlders  and  pebbles,  which  are  probably  derived 
from  the  basaltic  areas  high  tip  on  the  summits  of  the  Boise  Ridge, 
referred  to  later.  On  the  broad  flood  plain  of  Fall  Creek  the  bench 
gravels  are  very  extensive,  and  reach  an  elevation  of  4,380  feet  above 
the  sea,  or  50  feet  above  Fall  Creek.  All  of  the  benches  along  Granite 
Creek  and  its  tributaries  from  the  northeast  have  been  worked  for 
gold. 

Older  gravels. — Near  Placerville  and  Granite  are  several  very  inter- 
esting occurrences  of  gravels  belonging  to  a  stream  system  which  dif- 
fered considerably  from  the  present  one  and  giving  evidence  of  having 
undergone  disturbances  since  their  deposition.  Two  small  and  iso- 
lated gravel  patches  occur  close  together  one-fourth  mile  northwest  of 
Placerville,  on  Sailor  Gulch.  Each  contains  but  a  few  acres.  Both 
have  been  worked  by  the  hydraulic  process.  The  exposures  show  a 
30-foot  bank  of  medium-sized  gravel  with  excellent  fluviatile  stratifi- 
cation. The  gravel  contains  a  great  number  of  porphyry  bowlders 
similar  to  the  rock  cropping  near  Quartzburg.  The  granitic  bed  rock 
slopes  gently  westward,  and  extends  down  to  the  present  creek.  The 
bed  rock  is  150  feet  above  the  level  of  Wolf  Creek  at  Placerville.  A 
small  area  of  similar  gravel  lies  at  the  same  elevation  near  the  Pio- 
neerville  road,  1  mile  east-northeast  of  Placerville. 

Opposite  Placerville  lies  the  Ranch  Company's  claim,  which  has 
been  extensively  washed  of  late  years  and  has  produced  much  gold. 
This  is  a  mass  of  older,  compact  gravels  resting  in  a  channel-like 
depression,  and  on  which,  along  the  creek,  the  later  bench  gravels 
have  accumulated.  In  the  early  years  this  gravel  was  considered 
"false  bed  rock,"  and  it  was  not  generally  supposed  that  it  could  be 
profitably  worked.  The  gravel  body  lies  on  the  ridge  separating 
Boyles  Gulch  from  Wolf  Creek,  the  top  of  it  being  one-fourth  mile 
wide  and  reaching  an  elevation  of  200  feet  above  the  level  of  the  tail- 
ings at  Placerville.  It  fills  a  depression  or  channel,  the  bed  rock  ris- 
ing rapidly  northward  and  southward.  The  lowest  bed  rock  is  exposed 
in  the  present  diggings,  and  is  at  the  bank  75  feet  above  the  tailings 
at  Placerville,  sloping  from  there  gradually  down  to  the  debris-filled 
stream-bed  at  the  rate  of  6  feet  per  100  feet.  The  character  of  the 
gravel  is  shown  in  fig.  61.  The  gravels  bear  every  evidence  of  having 
been  accumulated  in  a  stream  of  considerable  size.  They  are  coarse 
at  the  bottom,  very  well  rounded,  and  contain  abundant  cobbles  of 
the  peculiar  altered  porphyry  occurring  near  Quartzburg.  No  basalt 
bowlders  were  found.  The  gold  is  fine  and  evenly  distributed  through 
the  mass  of  the  lowrer  gravel.  On  the  eastern  side  of  the  ridge  there 
are  also  hydraulic  pits,  and  the  deepest  bed  rock  lies  135  feet  above 
the  creek  bed  at  Placerville.  At  this  point  the  channel  suddenly 
18  GEOL,  PT  3 43 


674 


IDAHO    MINING    DISTRICTS. 


ceases.  Across  Ophir  Creek  the  bed  rock  rises  rapidly  in  all  direc- 
tions, and  no  possible  continuation  can  be  suggested  except  down  the 
narrow  canyon  of  Ophir  Creek.  Furthermore,  the  nature  of  the  peb- 
bles indicates  that  the  stream  came  from  some  point  to  the  northwest, 
whereas  the  present  grade  of  the  bed  rock  is  in  exactly  the  opposite 
direction.  The  conclusion  is  almost  unavoidable  that  the  channel 
has  been  cut  off  by  a  fault  and  its  grade  reversed. 

On  the  point  between  Wolf  Creek  and  Boyles  Gulch  a  little  of  the 
same  compact  gravel  occurs  just  at  the  edge  of  the  tailings.  Placer- 
ville appears  to  be  built  on  a  similar  compact  gravel,  in  which  narrow 
benches  were  cut  by  the  present  stream,  though  just  below  the  town 
granite  bed  rock  appears  at  the  edge  of  the  tailings.  Due  southwest 
of  Placerville,  on  the  slope  up  to  the  summit  of  the  level  ridge  between 
Granite  and  Wolf  Creek,  no  bed  rock  appears  to  have  been  found. 
Neither  has  there  been  any  bed  rock  found  on  the  opposite  slope  from 
this  ridge  down  to  Granite  Creek.  A  broad,  low  bench  fringes  the 
northeast  side  of  Granite  Creek  below  Granite.  Bed  rock  has  never 
been  found  for  some  distance  below  Granite  in  the  creek.  All  this 

appears  to  indicate 


I 


12    feef,  Granite  Sand 


8    feeh,  C/ay 
reef',  Coarse  Gravel 


FIG.  61.— Bank  at  the  Ranch  Company's  claim,  Placerville. 


that  the  Ranch 
Company's  channel 
continues  with  grad- 
ually sinkin'g  bed 
rock  across  Granite 
Creek. 

Interesting  c  o  n  - 
ditions  also  obtain 
across  Granite  Creek 
on  the  broad  flood  plain  of  Fall  Creek,  where  it  emerges  from  the  nar- 
row canyon  in  the  Boise  Ridge,  here  suddenly  rising  as  a  steep  escarp- 
ment facing  west.  This  place,  called  Norwegian  Flat,  at  present 
worked  by  the  Kennedy  Company,  is  extensively  covered  with  rich 
bench  gravels  up  to  the  mouth  of  the  canyon.  This  bench  gravel,  which 
is  rarely  over  25  feet  in  thickness,  does  not  rest  on  granite,  but  on  a 
harder,  more  compact  gravel,  which  contains  some  gold  and  which  is 
of  the  same  general  character  as  the  Ranch  Company's  gravel.  At 
the  upper  end  of  the  claim,  near  the  mouth  of  the  canyon  and  the  foot 
of  the  escarpment,  this  "false  bed  rock"  is  found  to  suddenly  abut 
against  the  granite,  strongly  suggesting  that  it  is  cut  off  by  a  fault. 
No  shafts  have  ever  been  sunk  in  this  lower  gravel.  It  is  probable 
that  it  is  the  same  channel  continuing  across  Granite  Creek,  and  that 
it  is  cut  off  at  both  ends  by  faulting.  On  the  hills  to  the  right  and 
left  of  Fall  Creek  a  similar  compact  gravel  also  occurs,  seemingly  con- 
tinuous with  that  of  the  deepest  chanuel.  Thus  the  low  ridge  between 
Fall  and  Canyon  creeks  is  covered,  up  to  an  elevation  of  80  feet  above 
Fall  Creek  at  the  upper  end  of  Kennedy's  claim,  and  a  similar  body 


IJNDGEEN.]         GRAVEL   AND    BASALT    OF    THE    BOISE    RIDGE.  675 

reaches  high  up  on  the  ridge  between  Fall  and  Granite  creeks  nearly 
to  the  Newburg  or  Lawyer  quartz  claim.  It  is  said  to  be  quite  rich 
here,  though  hard,  and  difficult  to  work  on  that  account  and  because 
of  the  scarcity  of  water.  On  this  ridge  the  older  gravel  distinctly 
rests  on  the  granite,  and  its  thickness  reaches  a  maximum  of  200  feet. 
Its  highest  elevation  on  the  ridge  near  this  quartz  mine  is  4,900  feet, 
or  500  feet  above  the  upper  end  of  Kennedy's  claim. 

Gravel  on  the  Boise  Ridge. — A  very  remarkable  occurrence  of 
gravel  was  found  on  the  summit  of  Boise  Ridge  3  miles  west-north- 
west of  Quartzburg.  The  broad,  flat  summit  extends  northward  from 
Hawkins  Pass,  with  a  winding  direction,  caused  by  the  deeply  incised 
gulches,  and  an  elevation  of  from  6,500  to  7,300  feet  above  the  sea. 
North-northwest  of  Quartzburg  lie,  on  the  summit,  several  hundred 
feet  of  scoriaceous  basaltic  flows,  which  extend  down  into  Jerusalem 
Valley  on  the  west.  In  this  basalt  there  occurs,  at  an  elevation  of 
6,900  feet,  one-half  mile  south  of  the  sharp  point,  with  an  elevation 
of  7,200  feet,  a  small  body  of  gravel.  It  could  not  be  determined 
whether  this  gravel  is  intercalated  between  the  basalt  beds  or  forms 
an  inclusion  in  the  same,  but  the  former  is  more  probable.  At  any 
rate,  the  gravel  is  well  washed,  of  granitic  character,  and  is  said  to 
contain  some  gold.  This  occurrence  is  of  the  greatest  interest,  as  it 
clearly  indicates  that  a  very  great  disturbance  has  taken  place  since 
the  eruption  of  these  basalts,  for  the  gravel  could  not  possibly  have 
been  formed  with  the  present  topographic  features.  Considered  in 
connection  with  the  faulted  old  gravels  at  the  eastern  foot  of  the 
escarpment,  2,700  feet  lower,  it  points  to  a  great  disturbance  along 
the  eastern  base  of  the  Boise  Ridge. 

Basalt. — The  whole  of  the  high  portion  of  the  Boise  Ridge  south  of 
the  latitude  of  Quartzburg  is  remarkably  free  from  any  late  erup- 
tions. At  the  locality  mentioned  in  the  preceding  paragraph,  culmi- 
nating in  the  hill  with  an  elevation  of  7,200  feet  north-northwest  of 
Quartzburg,  the  very  even,  flat  surface  of  the  granitic  ridge  is  capped 
by  300  feet  of  massive  basalt.  Above  the  massive  basalt  lie  200  feet 
of  tuff  and  scoriaceous  basalt,  again  covered  by  100  feet  of  fresh  and 
massive  olivine-basalt.  These  basaltic  flows  slope  rapidly  westward, 
and  the  ridge  on  the  north  side  of  Brainard  Creek  is,  as  seen  in  PI. 
LXXXIX,  composed  of  a  great  number  of  superimposed  thin  basaltic 
flows,  all  dipping  northwest  at  angles  of  30°  or  35°.  The  photograph  is 
taken  from  a  gap  in  the  ridge  between  Brainard  and  Porter  creeks,  3£ 
miles  west-southwest  from  the  high  basalt  peak  in  the  Boise  Ridge. 
Taken  in  connection  with  the  probable  fault  along  the  eastern  side  of 
the  range  at  Granite,  it  certainly  appears  as  if  a  westward  tilting  had 
formed  part  of  the  orographic  movements  in  this  vicinity  since  the 
time  of  the  deposition  of  the  lake  beds.  The  basalt  is  much  older 
than  the  basalt  of  the  lower  Moore  Creek,  and  in  all  probability  is 
contemporaneous  with  the  lake  beds. 


676 


IDAHO    MINING    DISTRICTS. 


Other  small  basalt  areas  were  noted  near  Hawkins  toll  road,  2  miles 
west  of  Star  Ranch.  This  basalt  forms  a  dike  on  the  high  ridge 
between  the  toll  road  and  Clear  Creek,  follows  the  road  for  some  dis- 
tance near  longitude  116°,  and  appears  again  on  the  ridge  north  of 
the  road.  Here  it  is  in  part  vesicular,  and  appears  to  have  flowed  out 
from  the  dike.  This  basalt  is  probably  also  of  Tertiary  age. 

FINENESS  OF  THE  GOLD. 

The  fineness  of  the  placer  gold  varies  from  770  to  912.  The  follow- 
ing list  gives  the  value  at  some  of  the  principal  localities : 

Value  and  fineness  of  placer  gold  at  principal  localities. 


Locality. 

Value  before 
melting. 

Fineness 
per  mill. 

Idaho  City  Turner's  claim  (bench  gravels) 

$16.  75 

Idaho  City,  East  Hill  (high  gravels) 

16.50  to  16.75 

Idaho  City,  Barker's  claim  (high  gravels) 

850 

Pioneerville  (bench  gravels)       

15.35 

770 

Placerville,  Ranch    Company   claim    (old 
channel  gravel)                                 .     

912 

Placerville  Granite  Creek  (bench  gravel) 

850 

Placerville,  Fall  Creek 

775 

Placerville,  Ophir  Creek      ..        .   

910 

Placerville,  Wolf  Creek  „  

910 

WATER  SUPPLY. 

The  water  available  for  placer  work  is  not  abundant;  in  fact,  usu- 
ally the  working  season  is  only  from  three  to  four  months.  The 
streams  are  not  large  and  do  not  head  among  very  high  mountains, 
so  that  the  flood  from  the  melting  snows  soon  subsides.  It  would  be 
possible,  but  hardly  practicable,  to  carry  a  ditch  to  the  basin  from 
the  headwaters  of  the  Boise  or  the  Payette.  The  principal  ditches 
are  as  follows : 

MOOEE   CREEK. 

1.  The  upper  Moore  Creek  ditch.     Takes  water  from  Moore  Creek  5  miles  above 

Gambrinus  Gulch.     Capacity,  600  miner's  inches. 

2.  The  Lambing  ditch.    Dam  below  Illinois  Gulch.     Capacity,  350  miner's  inches. 

3.  The  Christie  ditch.     Dam  above  mouth   of  Granite  Creek.      Capacity  1,100 

miner's  inches.    These  three  are  on  the  northwest  side  of  Moore  Creek. 

4.  Thorn  Creek  ditch.     Takes  its  water  from  Thorn  Creek,  dumping  it  across  the 

divide  into  Pine  Creek;  used  for  the  high  gravels  south  of  Idaho  City. 

5.  Channel  ditch.     Dam  on  Elk  Creek  one-half  mile  above  Elkhorn  Mill.     Capac- 

ity, 600  miner's  inches.     Covers  divide  between  Elk  and  Grimes  creeks. 

6.  Mann's  ditch.     On  south  side  of  Elk  Creek.     Dam  1  mile  above  Forest  King 

Gulch.     Ten  miles  long.     Covers  Gold  Hill  at  Idaho  City. 


LINDQREN.]  WATER    SUPPLY    AND    WORKABLE    GROUND.  677 

7.  Anderson  ditch.    Takes  water  from  Elk  Creek  below  Boulder  mine. 

8.  Cuddy  ditch.     Takes  water  from  Elk  Creek  below  Boulder  mine. 

9.  Dunn  ditch.    Takes  water  from  Elk  Creek  below  Boulder  mine. 

GRIMES   CREEK. 

The  water  supply  is  here  largely  controlled  by  the  Wilson  Company. 
The  principal  ditches  are  as  follows: 

1.  Wilson  ditch.    12  miles  long,  on  west  side  of  Grimes  Creek.     Dam  located  1 

mile  below  Charlotte  Gulch.     Capacity,  2,000  miner's  inches. 

2.  Gold  Trap  ditch.    7  miles  long,  also  on  west  side  of  Grimes  Creek. 

3.  American  ditch.     6  miles  long,  west  side  of  Grimes  Creek.     Dam  at  Charlotte 

Gulch. 

4.  Mountain  ditch.    8  miles  long,  west  side  of  Grimes  Creek.    Also  two  shorter 

ditches  from  Clear  Creek. 

GRANITE  CREEK. 

The  water  supply  is  here  controlled  by  the  Ranch  Company  and 
the  Kennedy  Company.  The  Ranch  Company's  ditch  is  14  miles  long, 
and  takes  water  from  Granite  Creek  above  Quartzburg.  Capacity, 
1 ,000  miner's  inches.  Other  ditches  lead  from  West  Fork,  Fall  Creek, 
and  Canyon  Creek. 

The  hydraulic  washings  use  a  pressure  of  from  100  to  350  feet. 
There  are  rarely  more  th/in  600  miner's  inches  used  in  each  monitor. 
Hydraulic  elevators  have  been  used  by  the  Wilson  Company  to  work 
low-bench  gravels  and  tailings.  The  gravel  is  elevated  from  10  to  25 
feet.  Five  hundred  miner's  inches  are  here  used  for  the  monitors. 

GROUND    AVAILABLE    FOR    FUTURE    WORK. 

The  largest  amounts  of  gravel  remaining  near  Idaho  City  are  on 
East  Hill  and  Gold  Hill.  Though  some  of  the  bench  gravels  remain 
they  are  getting  rapidly  worked  out.  In  the  Grimes  Creek  drainage, 
some  bench  gravels  still  remain  near  Pioneerville.  In  the  Granite 
Creek  drainage  there  is  a  considerable  area  of  low-bench  gravels  yet 
untouched  near  Granite,  on  both  sides  of  the  creek.  Considerable 
gravel  remains  at  the  Ranch  Company's  ground  near  Placerville.  If 
the  conclusions  in  this  paper  are  correct,  there  is  also  a  large  amount 
of  gravel  on  the  ridge  between  Wolf  Creek  and  Graniteville. 

In  all  three  drainage  branches  there  are  vast  amounts  of  tailings 
which,  with  suitable  appliances,  may  be  worked  over  again.  But 
there  is  no  doubt  that  the  placers  in  course  of  time  will  be  exhausted. 
That  they  are  not  already  exhausted  is  due  to  the  limited  water 

supply 

THE    MONAZITE   SANDS. 

The  sand  of  the  gravels  and  lake  beds  of  the  Idaho  Basin  is  entirely 
derived  from  the  granite  and  associated  dike  rocks.  It  consists  of 
relatively  angular  and  sharp-edged  grains,  indicating  its  manner  of 
formation  by  extremely  rapid  accumulation  from  ,the  deeply  disinte- 


678  IDAHO    MINING    DISTRICTS. 

grated  rocks.  The  heavy  minerals  found  in  the  granite  are  also 
found  in  the  sand,  and  may  be  easily  separated  by  washing  in  the 
miner's  pan;  they  are  always  deposited  in  the  sluice  boxes  with  the 
gold. 

In  all  parts  of  the  basin  a  yellow  or  brownish-yellow  mineral  forms 
a  considerable  quantity  of  the  heavy  substances  remaining  with  the 
gold.  It  is  usually  referred  to  as  "yellow  sand,"  and  is  also  given  the 
picturesque  name  of  "Bummer  Hill  sand,"  from  a  locality  near  Cen- 
terville,  where  it  was  particularly  abundant,  but  I  am  not  aware  that 
its  true  character  has  ever  been  investigated. 

The  mineral  has  been  shown  to  be  monazite,  this  being  the  first 
time  its  occurrence  has  been  noted  from  the  Western  States.  As  is 
well  known,  it  occurs  abundantly  in  the  granite  and  gneissoid  rocks 
and  gold-placer  mines  of  the  Southern  Appalachians,  and  in  several 
of  the  North  Atlantic  States,  also  in  Brazil,  the  Ural  Mountains,  and 
other  places.  There  is  no  doubt  that  it  forms  an  original  constituent 
of  the  granite  of  the  Idaho  Basin. 

One  of  the  samples  was  obtained  in  washing  a  few  pans  of  the  sandy 
lake  beds  occurring  as  "false  bed  rock"  in  a  gravel  bench  at  the 
junction  of  Moore  Creek  and  Granite  Creek,  3  miles  east  of  Idaho 
City  (see  fig.  59).  The  heavy  residue  consisted  largely  of  small  yellow 
grains  and  amounted  to  about  2  grams  per  pan  of  8  kilograms,  which 
would  correspond  to  0.025  per  cent.  The  microscope  revealed  the  fol- 
lowing minerals:  Ilmenite  in  sharp  hexagonal  crystals,  but  no  magne- 
tite; zircon,  also  in  extremely  sharp  crystals  of  a  slightly  brownish 
color,  and  abundant  yellow  or  greenish-yellow  grains  rarely  showing 
crystallographic  faces.  The  refraction  and  double  refraction  of  the 
latter  mineral  were  very  high;  the  hardness  not  much  over  5.  The 
ilmenite  was  eliminated  by  the  electro-magnet,  and  the  remaining  pow- 
der, containing  about  70  per  cent  of  the  yellow  mineral,  was  analyzed 
by  Dr.  W.  F.  Hillebrand.  The  result  showed  it  to  be  a  phosphate  of 
the  cerium  metals,  the  approximate  amount  of  the  oxides  of  the  latter 
being  48  per  cent;  in  these  approximately  1.20  per  cent  of  thoria  was 
found.  This  result  identifies  the  mineral  with  monazite,  the  only 
other  similar  mineral  being  xenotime,  which  is  mainly  a  phosphate  of 
yttrium  with  but  little  cerium.  The  samples  also  contained  a  con- 
siderable amount  of  titanium,  which  would  indicate  that  some  titanite 
is  present.  Practically  all  of  the  ilmenite  was  extracted  by  the 
magnet. 

Another  sample,  furnished  me  by  Mr.  T.  Myer,  of  Placerville, 
came  from  the  alluvial  gold  washings  in  Wolf  Creek,  near  that  town. 
Cleaned  from  quartz,  etc.,  it  appeared  as  a  heavy  dark  sand  consist- 
ing of  a  black  iron  ore  (ilmenite),  rounded  crystals  of  red  garnet, 
sharp  crystals  of  zircon,  and  irregular  grains  of  a  dark  yellowish- 
brown  mineral  with  waxy  luster,  sometimes  showing  crystallo- 
graphic faces.  It  was  found  impossible  to  extract  more  than  a  small 


THE    MONAZ1TE    SANDS.  679 

part  of  the  iron  ore  by  the  magnet.  There  was  practically  no  magne- 
tite present.  This  sand  was  examined  qualitatively  by  Dr.  Hille- 
brand,  who  found  phosphoric  acid,  cerium  metals,  and  thorium.  The 
yellowish-brown  material  is  therefore,  in  all  probability,  monazite. 

Monazite  has,  as  is  well  known,  a  certain  economic  value,  as  the 
oxides  of  the  rare  earths  contained  in  it  are  used  for  the  preparation  of 
the  incandescent  gaslights  of  the  Welsbach  and  other  burners.  A 
considerable  amount  of  monazite  sand  has  been  produced  during  the 
last  few  years  in  the  Southern  Atlantic  States,  chiefly  North  Caro- 
lina, and  in  Brazil.  The  prices  have  varied  from  3  to  25  cents  per 
pound,  according  to  the  purity  and  the  percentage  of  thoria.  The 
North  Carolina  monazite  contains  between  0.17  and  6.20  per  cent  of 
this  rare  earth.  Mr.  Waldron  Shapleigh,  chemist  for  the  Welsbach 
Light  Company,  kindly  gives  (March,  1897)  the  following  information 
in  regard  to  present  production  and  price: 

At  present  the  monazite  sand  market  is  very  dull;  hardly  any  demand,  and  only 
in  lots  of  a  few  tons.  The  present  price  in  North  Carolina  is  6  cents  per  pound, 
but  it  can  be  bought  a  little  lower  than  this.  Brazilian  sand  is  quoted  in  New 
York  at  4f  cents  per  pound,  fully  equal  to  the  North  Carolina  sand,  in  5  or  10  ton 
lots.  Larger  orders  can  be  placed  in  Brazil  at  a  much  lower  figure.  The  price 
has  been  steadily  downward,  as  the  supply  from  the  mines  now  opened  is  far 
greater  than  the  consumption.  It  is  not  generally  known  that  during  the  first 
eighteen  months  or  two  years  of  this  new  industry  enough  sand  was  mined  and 
purchased  by  the  largest  manufacturers  to  last  several  years  to  come,  as  so  far  it 
has  but  the  one  use.  The  manufacturers  did  not  know  how  extensive  the  sand 
deposit  was;  therefore  were  desirous  of  securing  a  large  and  safe  stock  at  the  start. 

The  largest  purchasers  are  the  Welsbach  Light  Company  of  Vienna,  supplying 
Europe,  and  the  Welsbach  Light  Company  of  Philadelphia,  which  supplies 
America.  I  should  hardly  think  that  Western  localities  could  compete  with 
North  Carolina  and  Brazil,  unless  the  mineral  is  of  a  very  superior  quality  or  a 
by-product. 

At  present  there  would  be  no  difficulty  in  placing  an  order  for  several  thousand 
tons  per  year  in  Brazil  and  having  it  filled. 

The  widespread  occurrence  of  monazite  in  considerable  quantities 
in  the  Idaho  Basin  raises  the  question  whether  the  deposits  can  be 
profitably  worked.  The  present  low  price  and  the  high  cost  of  trans- 
portation and  labor  make  this  very  doubtful,  unless  it  be  saved  as  a 
by-product  in  the  placer  mines.  It  will  be  necessary  to  extract  all 
ilmenite  by  strong  electro-magnets.  In  this  manner  a  comparatively 
pure  product  may  be  obtained.  It  is  not  practicable  to  entirely  sep- 
arate the  zircon  and  garnet  from  the  monazite.  The  purest  material 
was  obtained  from  near  Idaho  City,  while  that  from  Placerville  and 
vicinity  contains  a  large  amount  of  ilmenite  and  garnets.  Many  data 
in  regard  to  the  character  and  production  of  monazite  may  be  found 
in  a  paper  by  Mr.  H.  B.  C.  Nitze,  in  the  Sixteenth  Annual  Report  of 
the  United  States  Geological  Survey  (1894-95),  Part  IV,  pp.  G67-693. 


680  IDAHO   MINING   DISTRICTS. 


RELATION  BETWEEN  PLACERS  AND  QUARTZ  VEINS. 

The  dependence  of  the  gold  placers  upon  the  occurrence  of  gold- 
quartz  veins  is  very  strongly  brought  out  by  a  study  of  the  occurrences 
of  both.  While  there  are  many  small  quartz  seams  occurring  through- 
out the  granite,  some  of  which  may  contain  a  little  gold,  it  is  perfectly 
evident  that  there  are  two  regions  in  which  quartz- vein  deposits  are 
concentrated.  These  are,  first,  the  Gambrinus  mining  district,  on 
the  ridge  between  Elk  Creek  and  Moore  Creek,  continued  by  the  Elk- 
horn  mining  district,  at  the  headwaters  of  Elk  Creek;  and  second, 
the  gold  belt  extending  from  the  Boise  Ridge  near  Quartzburg  to 
Grimes  Pass.  Every  creek  and  ravine  leading  up  to  these  .deposits 
has  been  rich,  while  the  watercourses  rising  in  other  parts  of  the 
range  are  comparatively  barren.  It  seems  clear  beyond  doubt  that 
most  of  the  gold  in  the  gravels  near  Idaho  City  came  down  the  Illinois 
and  Gambrinus  gulches;  above  these  Moore  Creek  becomes  compara- 
tively poor.  What  gold  there  is  has  doubtless  been  derived  from  the 
more  distant  veins  at  the  very  head  of  Moore  Creek,  near  Summit 
Flat.  In  nearly  every  case  an  exceptionally  rich  ravine  has  been 
found  to  lead  up  to  a  quartz  vein.  Thus  it  is  clear  that  the  recently 
discovered  Summit  mine,  on  the  ridge  between  Elk  and  Grimes  creeks, 
furnished  the  gold  found  in  Deer  Creek  and  Henry  Creek.  The  only 
occurrence  to  which  some  doubt  is  attached  as  to  the  derivation  of 
the  gold  is  that  of  the  rich  angular  gravels  at  the  head  of  Spanish 
Fork  and  Willow  Creek,  but  it  is  probable  that  they  are  derived  from 
local  seams  and  veins. 

The  headwaters  of  Grimes  Creek  furnish  a  most  convincing  argu- 
ment in  favor  of  the  derivation  of  the  gold  from  the  quartz  belt. 
Every  gulch  heading  along  the  line  of  that  belt  is  rich,  while  every 
one  not  crossing  it  carries  only  extremely  small  quantities  of  gold. 

The  conclusion  is  that  practically  all  of  the  placer  gold  in  the  dis- 
trict has  been  derived  from  the  quartz  Veins  in  these  two  districts. 

On  an  average  the  fineness  of  the  gold  in  the  quartz  veins  is  a  little 
less  than  that  in  the  placers.  This  has  generally  been  the  experience 
in  most  mining  districts,  and  is  accounted  for  by  a  dissolving  of  the 
silver  and  baser  metals  from  the  surface  of  each  grain  of  gold.  The 
highest  grade  of  quartz  gold  is  found  near  Quartzburg,  and  in  the 
gravels  of  Placerville,  derived  from  the  Quartzburg  mines,  the  placer 
gold  is  of  unusual  fineness. 


CHAPTER   IV. 

THE  IDAHO  BASIN  (CONTINUED). 

THE  PRE-TERTIARY  ROCKS. 
GRANITE. 

The  Idaho  Basin  forms  a  part  of  the  great  granite  area  of  the  Boise 
and  Payette  drainage,  and  the  pre-Tertiary  rocks  consist  exclusively 
of  granite,  together  with  a  number  of  porphyritic  dikes,  probably 
intruded  shortly  after  the  granitic  intrusion.  It  has  been  stated 
before  that  the  age  of  this  granite  is  unknown.  If  Archean,  as  has 
been  supposed,  the  slight  amount  of  compression  and  change  it  has 
undergone  is  certainly  remarkable.  A  shearing  is  often  noticeable, 
dividing  the  rock  into  sheets  or  plates  upward  of  a  foot  thick.  The 
direction  of  the  shearing  varies  considerably,  and  is  sometimes  paral- 
lel to  the  general  direction  of  the  quartz  vein.  In  Gambrinus  and 
Sub-Rosa  gulches  a  strike  of  -N.  20°  to  24°  W.  and  a  dip  of  70°  E.  or  W. 
were  noted.  In  the  Ranch  Companj^'s  claim  at  Placerville  the  sheet- 
ing is  parallel  to  the  direction  of  the  Quartzburg  gold  belt;  strike,  N. 
45°  E. ;  dip,  60°  SE.  On  Hawkins  toll  road,  on  the  western  slope  of 
the  Boise  Ridge,  the  strike  is  N.  60°  to  70°  W.  and  the  dip  70°  to  80°  N. 
or  S.  Conjugated  systems  of  shear  planes,  having  the  same  strike, 
but  dipping  in  opposite  direction,  thus  occur  here.  In  the  depres- 
sions and  low  ridges  of  the  basin  the  granite  is  disintegrated  to  con- 
siderable depth,  so  that  it  is  very  difficult  to  secure  good  specimens. 
The  disintegrated  granite  forms  a  coarse,  yellowish-gray  sand,  the 
individual  grains  of  which  have  undergone  but  very  little  decompo- 
sition, and  which  is  easily  swept  down  into  the  creeks  by  the  rain 
storms.  Fresher  and  harder  rocks  crop  out  on  the  high  ridge  between 
Elk  and  Moore  creeks,  upon  which  the  Forest  King  and  other  mines 
are  located.  The  outcrops  form  brilliant  white  rounded  masses ;  but 
even  here  the  disintegration  has  made  rapid  progress.  On  the  Boise 
Ridge  the  granite  is  ordinarily  soft  and  crumbling.  The  deepest 
disintegration  is  probably  found  about  the  head  of  Muddy  and  Ophir 
creeks,  where  a  good  outcrop  is  only  rarely  seen.  The  granite  area 
extends  northward  across  the  Payette  River  and  far  to  the  north  of  it. 

The  granite  has  a  coarse  grain,  the  average  size  of  the  constituents 
being  3nim.  The  reddish  orthoclase  crystals  are  often  very  prominent. 

681 


682  IDAHO    MINING    DISTRICTS. 

The  rock  is  composed  of  gray  quartz,  white  or  reddish  feldspar — 
partly  orthoclase,  partly  an  acid  soda-lirne-feldspar — and  small  biotite 
flakes,  the  incipient  decomposition  of  which  usually  gives  the  rock  a 
rusty  aspect.  Hornblende  is  rarely  found.  Muscovite  often  occurs 
in  the  more  acid  varieties.  Of  accessory  constituents,  which  are  best 
studied  by  washing  the  decomposed  sandy  granite,  there  are:  Ilmen- 
ite  in  often  perfect  crystals  (though  little  or  no  magnetite  appears  to 
be  present),  apatite,  zircon  in  extremely  sharp,  slightly  brownish 
crystals,  small  garnets,  titanite,  and  brownish  or  yellowish  imperfect 
crystals  of  monazite.  For  description  of  the  monazite  sands,  see  pp. 
677-679. 

DIKES   ASSOCIATED    WITH   THE    GRANITE. 

The  granite  is  traversed  by 'dikes,  which  in  some  places  become 
very  numerous  and  large.  Dikes  of  granite-porphyry  and  aplite  are 
common,  though  rarely  very  long  and  wide.  Many  such  dikes,  to- 
gether with  others  of  pegmatitic  character,  occur;  for  instance,  along 
the  road  southwest  of  Idaho  City  and  on  the  hill,  with  an  elevation  of 
6,200  feet,  due  south  of  the  town. 

Dark-colored,  lamprophyric  dike  rocks,  which  generally  belong  to 
the  minettes,  were  noted  in  a  few  localities.  These  dikes  are,  as  a 
rule,  narrow,  and  their  occurrence  is  closely  connected  with  that  of 
the  veins.  From  the  Sub-Rosa  and  Forest  King  mines  dark-gray,  fine- 
granular  dike  rocks  were  collected,  generally  rich  in  black  inica. 
In  thin  section  the  former  appears  as  typical  minette,  consisting  of 
biotite,  augite,  magnetite,  and  orthoclase,  with  pauidiomorphic  struc- 
ture. The  feldspar  crystals  show  a  tendency  to  radial  or  spherulitic 
arrangement.  A  similar  minette,  consisting  of  biotite,  hornblende, 
and  orthoclase,  was  collected  at  the  Gold  Dollar  tunnel,  1,000  feet  east 
of  the  pass  leading  from  Placerville  to  Garden  Valley.  The  dikes 
evidently  antedate  the  veins. 

The  Bois"e  Ridge  south  of  Quartzburg  contains  scattered  dikes  of 
granite-porphyry  and  diorite-porphyrite,  but  near  the  latter  locality 
begins  a  very  important  belt  of  dikes  intimately  connected  with  the 
Quartzburg  belt  of  gold  deposits.  The  rocks  are  in  all  respects  simi- 
lar to  those  which  appear  at  Willow  Creek  mining  district;  the  latter 
may  in  fact  be  regarded  as  the  westward  extension  of  the  Quartzburg 
belt,  having  the  same  direction  and  lying  in  its  continuation  to  the 
west-southwest,  but  a  distance  of  8  miles,  barren  of  mineral  deposits 
and  dikes,  separates  them.  The  dikes  do  not  follow  the  mineral 
deposits  in  detail  and  are  very  irregular,  sometimes  only  a  few  hun- 
dred feet  wide,  then  again  expanding  to  a  width  of  over  a  mile. 
Owing  to  unusually  deep  residuary  soil  on  the  divide  toward  Payette 
River,  the  contact  of  granite  and  porphyries  is  generally  difficult  to 
trace,  and  the  areal  extent  indicated  on  PI.  XCVI  must  be  regarded 
as  only  approximately  correct. 


LI.VDGREN.]  DIKES    ASSOCIATED    WITH    THE    GRANITE.  683 

The  porphyry  begins  at  the  Mountain  Chief  and  Belzazzar  mines, 
where  it  occurs  as  a  wide  belt  extending  across  the  vein  and  forming 
a  considerable  part  of  the  hill  to  the  east  of  the  mines.  Large  masses 
of  a  similar  porphyry  occur  in  the  lower  part  of  Fall  Creek,  and  it 
continues  eastward  toward  Quartzburg  as  a  narrowing  belt.  The 
rock  in  this  area  is  a  characteristic  light-colored  hornblende-porphy- 
rite,  consisting  of  white  plagioclase  in  stout  prisms  up  to  lcm  long, 
and  idiomorphic  hornblende  crystals  up  to  5ram  in  length,  embedded 
in  a  fine-grained  groundmass  of  feldspar,  hornblende,  and  a  little 
quartz. 

At  Quartzburg  the  porphyry  belt  is  only  a  few  hundred  feet  wide 
and  has  undergone  great  thermal  alteration,  secondary  minerals  like 
pyrite,  muscovite,  and  calcite  being  abundant.  On  the  Gold  Hill 
mine  dump  specimens  of  fairly  fresh  rocks  were  collected.  Some  of 
them  are  very  similar  to  the  above-described  rock.  The  abundant 
large  white  feldspars  are  labradorite,  according  to  extinction  of 
numerous  Carlsbad  twins.  There  is  no  hornblende  left  undecom- 
posed,  but  there  is  some  light-brown  biotite  in  process  of  conversion 
to  chlorite.  The  groundmass  is  micropoikilitic,  consisting  of  quartz 
and  unstriated  feldspar.  Another  variety,  greatly  altered,  of  a  yel- 
lowish color  and  impregnated  with  pyrite,  is  characterized  by  large 
corroded  quartz  crystals,  up  to  lcm  in  diameter,  and  large  porphy- 
ritic  labradorite,  greatly  altered  by  sericitization.  The  groundmass 
is  fine-granular,  probably  micropoikilitic,  of  quartz  and  feldspar,  but 
now  greatly  filled  with  sericite. 

East  of  Gold  Hill  the  porphyry  belt  widens  considerably.  Quartz- 
burg Hill  is  composed  of  quartz-diorite-porphyrite.  This  rock,  similar 
to  that  described  from  the  Belzazzar  mine,  forms  the  largest  part  of 
the  area.  It  crosses  Wolf  Creek  as  a  wide  belt,  and  is  here  accom- 
panied by  dikes  of  more  basic  rocks.  Two  miles  north  of  Placerville 
a  dike  of  norite-gabbro  crosses  the  road  and  a  dike  of  normal  diabase 
appears  in  the  same  vicinity.  East  of  Wolf  Creek  the  area  widens 
still  more  and  reaches  its  maximum  width.  At  Sweet's  Claim,  one- 
half  mile  west  of  Grimes  Pass,  the  porphyry  is  narrower.  A  specimen 
from  the  Northern  Star  shaft  shows  the  same  idiomorphic  large  feld- 
spar and  hornblende  crystals.  The  former  are  very  fresh  and  consist 
of  labradorite ;  the  latter  are  sharply  idiomorphic  and  partly  chlori- 
tized.  The  groundmass  is  microcrystalline  allotriomorphic,  being 
made  up  of  quartz  and  unstriated,  clouded  feldspar. 

This  porphyry  belt  was  not  followed  east  of  Grimes  Pass,  but  it  is 
apparent  that  it  attains  great  development  among  the  high  hills  rising 
beyond  it.  Clear  Creek  contains  a  great  abundance  of  porphyiy 
bowlders.  They  are  practically  the  same  quartz-diorite-porphyrite 
which  is  described  above.  Quartz  is  evidently  always  present  in  the 
groundmass,  and  sometimes  also  as  porphyritic  crystals. 


684  IDAHO    MINING    DISTRICTS. 

THE   QUARTZ   VEINS. 
THE  IDAHO   CITY  GOLD  BELT. 

In  the  immediate  vicinity  of  Idaho  City  very  few  quartz  veins  occur, 
and  none  of  importance.  Mr.  Plowman  states  that  a  big  quartz  vein 
was  found  on  Wallula  Flat,  2  miles  east  of  Idaho  City,  on  the  northern 
side  of  the  creek.  A  narrow  streak  in  this  vein  carries  gold.  About 
1  mile  due  south  of  Idaho  City  the  Keystone  mine  was  located  on  a 
large  but  apparently  barren  vein. 

Six  miles  northeast  of  Idaho  City,  on  the  ridge  between  Moore 
Creek  and  Elk  Creek,  is  the  Gambrinus  mining  district. 

The  Elaine  vein  is  situated  on  the  Moore  Creek  side  of  the  ridge. 
The  developments  are  small,  though  some  fair  ore  has  been  extracted 
and  milled.  There  is  a  5-stamp  mill  on  the  property. 

The  Chickahominy  vein  lies  a  little  higher  up  on  the  ridge  and  a 
few  hundred  feet  south  of  the  Blame.  It  was  worked  in  the  early 
days,  and  a  large  mill  was  erected  on  Moore  Creek  4£  miles  above 
Idaho  City. 

The  Illinois  vein. — This  important  deposit,  which  can  be  traced  for 
If  miles,  is  located  three-fourths  of  a  mile  above  the  Blaine,  and 
crosses  the  ridge  at  an  elevation  of  5,100  feet.  The  vein  has  an  aver- 
age strike  of  a  few  degrees  north  of  west  and  dips  to  the  south  at  an 
angle  of  from  45°  to  50°.  It  is  inclosed  in  granite  throughout,  though 
smaller  dikes  of  porphyry  occur  occasionally  in  this  granite.  The 
vein  is  one  of  the  strongest  in  the  basin,  and  it  is  very  clear  that  it 
has  furnished  a  large  portion  of  the  placer  gold  in  Moore  Creek.  It 
contains  a  great  deal  of  finely  distributed  gold  all  along,  and  some 
good  pay  shoots  besides.  Illinois  Gulch,  draining  this  vicinity,  is 
reported  to  have  been  extraordinarily  rich. 

The  Eureka  claim  lies  at  the  eastern  end  of  the  vein.  Its  production 
amounts  to  $30,000,  and  besides  much  was  taken  from  surface  diggings 
near  the  vein.  A  10-stamp  mill  stands  on  the  claim,  which  has  not 
been  worked  since  about  1880.  The  vein  is  a  large,  composite  one, 
similar  to  the  Illinois,  to  be  described  later.  At  the  time  of  its 
exploitation  an  ore  shoot  in  this  vein  was  worked  down  to  a  small 
depth,  where  it  is  said  to  have  been  lost.  The  developments  are 
slight,  consisting  only  of  a  tunnel  and  a  shaft  60  feet  deep. 

The  Lucky  Boy  adjoins  on  the  west.  The  developments  consist  of 
only  a  few  prospect  holes.  The  strike  is  N.  81°  W.  and  the  dip  50°  S. 
The  exposures  show  8  feet  of  decomposed  and  sheeted  granite,  with 
small  quartz  seams.  Some  pay  ore  is  found  on  the  foot  wall.  Two 
parallel  veins  exist,  one  30  feet  south  and  the  other  200  feet  north  of 
the  main  fissure. 

The  Illinois,  consisting  of  two  claims,  is  the  principal  producer  of 
the  vein.  It  was  located  in  the  early  days,  as  it  was  soon  seen  that 


LINDGEEN.]  IDAHO    CITY    GOLD    BELT  685 

the  rich  placers  led  up  to  the  vein.  The  production  is  stated  to  be 
$225,000,  which  has  been  chiefly  taken  out  in  small  batches  of  very 
rich  ore.  Some  ore  from  this  claim  was  crushed  in  1895  in  the  Elaine 
mill.  The  deposit  is  characteristic  of  many  veins  in  the  Idaho  Basin. 
Large  masses  of  quartz  are  hardly  ever  seen.  The  strike  is  N.  71°  W. 
and  the  dip  40°  S.  The  vein  consists  of  a  wide  zone  of  sheeted  and 
fractured  granite,  with  abundant  small  quartz  seams  between  the 
joints  of  the  sheets  or  ramifying  through  them.  These  small  quartz 
seams  carry  the  gold,  while  the  granite  between  them,  though  usually 
altered,  soft,  and  decomposed,  contains  no  pay.  This  sheeted  zone 
is  here  30  to  40  feet  wide  and  contains  gold  throughout.  The  princi- 
pal pay  shoot  is,  however,  400  feet  long,  and  one  streak,  2  feet  wide, 
in  this  pay  shoot  is  particularly  rich.  The  deposit  has  been  sluiced 
off  on  the  surface  and  then  worked  by  means  of  a  crosscut  tunnel 
from  the  gulch.  A  cross  seam,  also  carrying  some  gold,  joins  it  in 
Illinois  Gulch,  and  a  parallel  vein  is  also  said  to  exist.  The  ore  is 
practically  all  free  milling  on  the  surface.  Even  when  sulphurets 
are  met  with  in  depth  it  is  probable  that  a  larger  proportion  of  the 
gold  will  remain  in  free  condition.  The  developments  may  be  said  to 
be  very  slight  and  unsatisfactory,  but  it  is  probable  that  if  properly 
opened  the  vein  would  furnish  great  amounts  of  low-grade  ore,  which, 
with  suitable  and  cheap  methods  of  extraction  and  reduction,  might 
be  made  to  pay.  The  width  of  the  vein  and  the  soft  character  of  the 
rock  would  make  mining  somewhat  expensive  and  difficult. 

The  Chicago  claim,  on  which  but  a  slight  amount  of  development 
work  has  been  done,  adjoins  on  the  west,  beginning  near  the  road  on 
the  summit  of  the  ridge. 

The  Populist  vein. — This  vein  is  situated  1  mile  west-northwest  of 
the  Illinois.  It  has  a  similar  strike  and  dip,  and  some  work  has  been 
done  on  it  recently. 

The  Cleveland  vein. — This  relatively  small  vein  is  locHted  5  miles 
north-northwest  of  Idaho  City,  on  the  south  side  of  Forest ,King  Gulch, 
at  an  elevation  of  5,030  feet.  It  is  a  single-fissure  vein,  about  1  to  2 
feet  wide,  inclosed  in  granite,  striking  a  little  north  of  west  and  dip- 
ping 60°  S.  A  rich  shoot  100  feet  long  was  found  on  it  a  few  years 
ago,  which  yielded  a  considerable  sum  of  money;  it  has  not  been 
followed  below  the  present  tunnel  level.  The  mine  is  of  interest  as 
showing  plainly  the  result  of  faulting,  illustrated  in  fig.  62.  The  vein 
is  thrown  a  distance  of  GO  feet  horizontally  in  the  hanging  wall.  At 
least  two  faults  of  this  character  are  known.  If  movements  in  only 
a  vertical  direction  have  taken  place,  this  fault  is  certainly  an  over- 
thrust,  the  hanging  wall  having  moved  up  relatively.  As,  however, 
lateral  movements  may  also  have  occurred,  it  is  possible  that  the 
present  position  of  the  vein  may  be  due  to  an  oblique  movement  to 
the  southwest,  the  direction  of  which  makes  with  the  horizontal  an 
angle  of  between  0°  and  60°,  the  hanging  wall  having  moved  down 


686 


IDAHO    MINING   DISTRICTS. 


relatively.     While  this  is  possible,  the  probabilities  are  strongly  in 
favor  of  an  overthrust. 

Tlie  Gambrinus  (Surprise]  vein. — This  large  deposit  is  situated  5^ 
miles  north-northeast  of  Idaho  City,  on  the  summit  of  the  ridge 
between  Elk  and  Moore  creeks  and  near  the  foot  of  the  steep  Forest 
King  Hill.  The  elevation  is  5,480  feet.  It  was  discovered  in  1864, 
and  the  principal  work  was  done  between  1864  and  1865.  The  total 
production  is  $263,000.  The  strike  of  the  vein  is  N".  61°  W.,  and  the 
dip,  measured  on  the  exposed  foot  wall,  is  45°  S.  It  can  be  traced  for 
some  distance  westward,  and  the  Buckeye  forms  the  western  exten- 
sion. The  vein  has  a  maximum  width  of  40  feet,  and  isjof  the  same 
composite  type  as  the  Illinois,  consisting  of  a  sheeted  zone  in  granite 
with  a  great  many  small  and  rich  quartz  seams  between  the  joints, 
these  seams  containing  all  the  pay.  The  surface  is  very  greatly 
decomposed  arid  has  been  extensively  sluiced.  Two  chimneys  or 
shoots  of  rich  ore  were  found  close  together,  dipping  east  on  the  plane 
of  the  vein,  at  first  steep  and  then  more  gentle.  These  shoots  were  not 

nearly  so  long  as  the  Illi- 


Norfh 


• 


r 

°^ 


Vein 


^. 


Vein 


rOrifr 


7 


FIG.  62.— Diagram  of  fault  in  the  Cleveland  vein. 


nois  ore  body,  but  richer. 
The  ore  contains  antimo- 
nite,  and  this  mineral  ap- 
pears to  be  closely  associ- 
ated with  the  gold.  The 
vein  has  been  developed 
only  by  short  tunnels  and 
small  shafts,  riot  over  100 
feet  deep,  and  appears, 
like  the  Illinois,  to  deserve 
much  more  extensive  pros- 
way  of  water  and  heavy 


pecting.     The    same    difficulties  in   the 
ground  will  probably  be  met  with  in  depth. 

The  Boulder  vein. — This  deposit  is  located  on  Elk  Creek,  6£  miles 
north  by  east  of  Idaho  City,  at  an  elevation  of  4,830  feet.  Prepara- 
tions were  made  a  few  years  ago  to  exploit  this  vein  on  a  large  scale, 
and  an  excellent  30-stamp  mill,  to  be  driven  by  water  power,  was 
built.  It  was  run  for  only  a  short  time,  the  ore  probably  being  of 
too  low  grade  to  handle  profitably;  neither  was  there  much  ore  in 
sight,  so  that  it  would  have  been  necessary  to  sink  below  the  creek 
level  almost  immediately.  The  vein,  which  crops  for  only  a  short 
distance  and  is  marked  on  the  canyon  slope  by  quartz  croppings  sev- 
eral feet  thick,  strikes  on  the  surface  N.  75°  W.  and  dips  50°  S.  It  is 
opened  by  a  tunnel  900  feet  long.  The  general  character  is  the  same 
as  the  Gambrinus  and  the  Illinois,  being  a  very  wide  (up  to  40  or  even 
60  feet)  zone  of  sheeted  granite  filled  with  many  small  seams  of  quartz 
carrying  pyrite,  arsenopyrite,  and  zincblende  scattered  through  it. 
As  it  was  necessary  to  mine  the  whole  width,  though  the  pay  was 


LINDOREN.]  IDAHO    CITY    GOLD    BELT.  687 

only  in  the  narrow  seams,  and  as  the  ground  was  very  soft  and  heavy, 
square  timbering  had  to  be  used.  Underground  the  vein  appears  to 
strike  N.  20°  W.,  from  which  disagreement  with  the  surface  strike  it 
would  appear  that  the  vein  has  been  considerably  disturbed.  A  nar- 
row vein  in  the  hanging  wall  of  the  big  deposit  was  mined  during 
189G  and  furnished  small  quantities  of  very  rich  ore.  This  was  not 
much  decomposed,  and  indicated  what  the  character  of  the  ore  will 
be  in  depth.  It  contained  bunches  of  pyrite,"  arsenopyrite,  and 
blende,  with  a  gangue  of  quartz  and  some  calcite.  The  fresh  sul- 
phurets  contained  much  coarse  gold,  the  ore  being  free  milling  to  70 
per  cent  of  its  value.  It  is  probable  that  most  of  the  vein  in  the 
Crambrinus  mining  district  will  remain  largely  free  milling  as  depth 
is  attained.  The  value  of  the  coarse  gold  in  the  sulphurets  is  $15  to 
$10.  The  fineness  of  the  amalgamated  bullion  is  680  to  718. 

Mona  MacCarthy  is  the  name  of  a  small  vein  located  three-fourths 
of  a  mile  west  of  the  Boulder,  on  the  high  side,  and  lying  between  the 
Boulder  and  the  Forest  King  veins.  Some  work  has  been  done  on  it. 
Many  small  seams  are  found  between  this  vein  and  the  Forest  King. 

The  Sub-Rosa  or  Forest  King  vein. — This  vein  is  traceable  for  a 
distance  of  2  miles  from  the  Washington  mine  on  the  east  to  beyond 
the  Forest  King  on  the  west.  It  crops  in  hard  granite  throughout, 
though  at  several  places  dark-green,  dioritic  dikes  appear  near  it  or 
cross  it.  Though  narrower  than  the  Illinois  and  the  Gambrinus,  it 
has  produced  some  good  pay  shoots. 

The  Forest  King  was  located  in  1875,  and  a  10-stamp  mill  was  erected 
on  it  in  1884.  The  elevation  of  the  mill  is  6,280  feet.  The  United 
States  mineral  monument  of  the  district  is  indicated  by  an  iron  rod  in 
an  outcrop  close  by.  No  work  has  been  done  on  the  vein  during  the 
last  few  years.  The  vein  shows  on  the  surface  in  quartzose  crop- 
pings,  which  do  not  contain  any  pay.  It  is  opened  by  a  tunnel  900 
feet  long,  through  granite,  which  shows  several  seams  dipping  south- 
ward. The  vein  consists  of  a  zone,  several  feet  wide,  of  crushed  gran- 
ite with  smaller  quartz  seams.  It  strikes  N.  56°  W.,  and  dips  60°  S. 
The  drift  on  the  vein  extends  several  hundred  feet  east  and  west. 
Three  hundred  feet  west  a  dike,  20  feet  wTide,  of  a  dark,  syenitic  rock 
(probably  a  minette)  apparently  cuts  across  the  vein ;  but  from  the 
fact  that  the  dike  is  full  of  small  quartz  seams,  which  all  contain  a 
little  gold,  it  is  probable  that  the  dike  is  really  older  than  the  vein, 
and  that  the  difference  in  appearance  of  the  vein  in  the  two  rocks  is 
due  to  the  difference  in  their  resistance  to  the  dislocating  force.  A 
dike  of  the  same  rock,  1  foot  wide,  occurs  in  the  crosscut,  and  is  par- 
allel to  the  vein  in  dip  and  strike.  A  50-foot  winze  was  sunk  below 
the  tunnel  level,  some  distance  west  of  the  crosscut,  in  the  bottom  of 
which  was  found  altered  granite,  with  sulphurets  and  small  quartz 
seams,  giving  assay  values  of  $80  to  $100  per  ton. 

A  location  called  the  Northern  Light,  on  which  some  work  has  been 


688  IDAHO    MINING    DISTRICTS. 

done,  adjoins  the  Forest  King  on  the  east.  The  Sub-Rosa,  also  called 
the  Confederate,  is  a  claim  on  the  same  vein,  1,500  feet  long,  and 
located  on  the  steep  side  hill  toward  Moore  Creek.  The  topography 
is  very  rugged,  owing  to  the  depth  to  which  the  gulches  have  been 
incised  in  the  granite.  At  the  line  between  the  Sub-Rosa  and  the 
Washington  the  elevation  is  5,500  feet.  The  vein  was  worked  many 
years  ago  by  Mr.  William  Hooten,  who  extracted  a  considerable 
amount  of  very  high  grade  ore  from  a  comparatively  small  shoot. 
Then  the  mine  lay  idle  for  many  years,  until  1896,  when  work  was 
resumed  with  the  intention  of  finding  the  continuation  of  the  pay 
shoot  from  a  lower  tunnel  level.  The  strike  of  the  vein  is  N.  56°  W., 
and  the  dip  is,  as  usual,  to  the  south.  The  vein  is  several  feet  thick, 
consisting  of  a  very  soft  clayey  mass  of  altered  granite  with  quartz 
seams.  Many  smaller  dikes  of  lamprophyric  rocks,  chiefly  minettes, 
occur  near,  the  vein.  In  one  of  the  older  tunnels  it  is  clearly  seen 
how  one  of  these  dikes  is  sharply  cut  off  and  faulted  by  the  vein. 
The  exposures  in  the  lower  tunnel  of  1896,  300  feet  below  the  old 
workings,  are  interesting.  A  small  portion  of  the  vein  was  found  in 
about  normal  position,  but  on  following  it  toward  the  west,  in  the 
direction  of  the  ore  shoot,  it  was  found  to  be  cut  off  by  a  dike  of 
minette  20  to  30  feet  wide,  across  which  solid  granite  again  was  met. 
At  first  glance  it  would  appear  as  if  a  later  dike  had  cut  across  the 
vein  and  faulted  it,  but  upon  close  inspection  of  the  dike  it  is  seen 
to  be  extremely  crushed  and  separated  from  the  vein  by  fault  planes, 
and  the  probability  is  that  the  dike  was  intruded  before  the  vein  was 
formed,  and  that  a  subsequent  fault  has  thrown  the  vein  in  the  hang- 
ing wall,  just  as  happened  in  the  Cleveland  vein.  This  is  made  the 
more  probable  as  extensive  explorations  had  previously  failed  to  find 
it  in  the  foot  wall. 

The  Washington  claim  adjoins  the  Sub-Rosa  on  the  east.  This 
part  of  the  vein  was  exploited  a  few  years  ago,  and  a  considerable 
amount  of  gold  was  extracted.  The  mine  is  equipped  with  a  10-stamp 
mill,  and  is  developed  by  a  tunnel  following  the  vein  for  290  feet  and 
a  vertical  shaft  sunk  to  316  feet  at  the  mouth  of  the  tunnel;  three 
levels  are  turned  from  the  shaft,  and  extend,  the  first  to  400,  the  sec- 
ond to  250,  and  the  third  to  170  feet  toward  the  east.  The  vein  is 
vertical,  and  has  about  the  same  strike  as  the  Sub-Rosa.  An  ore 
shoot  45  feet  long  and  from  1  to  6  feet  thick  was  found,  and  has  been 
stoped  from  the  200-foot  level  up  to  the  surface.  The  yield  is  reported 
to  have  been  $90,000  from  4,300  tons,  or  $20  per  ton.  The  ore  was 
practically  all  free-milling  and  consisted  of  fresh  quartz.  A  little 
pyrite  occurred  in  depth.  The  shoot  was  cut  off  in  depth  by  a  small 
vein  carrying  silver,  and  its  continuation  beyond  this  is  not  known. 
Forty  feet  north  of  the  gold  vein,  and  separated  from  it  by  altered 
granite,  is  a  strong  vein  of  solid  quartz,  from  8  inches  to  4  feet  wide, 
which  has  been  exposed  by  crosscuts  from  all  levels.  This  vein 


LINDGEEN.]  IDAHO   CITY   GOLD    BELT.  689 

carries  silver  only — as  chloride  on  top,  stephanite  and  ruby  silver  in 
depth — the  average  assays  showing  values  of  from  33  to  90  ounces  per 
ton.  Ore  of  the  latter  kind  carries  only  $1  of  gold.  Though  much  of 
this  silver  ore  is  in  sight,  none  has  yet  been  extracted.  Four  hun- 
dred and  fifty  feet  beyond  the  breast  of  the  tunnel  another  ore  body 
is  said  to  show  on  the  surface  and  to  carry  both  gold  and  silver.  This 
is  one  of  the  few  occurrences  of  silver  veins  in  the  basin,  and  is  of 
great  interest,  as  the  two  veins  evidently  represent  separate  periods 
of  vein  filling,  the  silver  vein  probably  being  the  later. 

The  Elkhorn  mining  district  adjoins  the  Gambrinus  and  is  situated 
on  upper  Elk  Creek. 

The  Elkhorn  vein  is  an  old  location  at  the  junction  of  Elk  Creek 
and  Ross  Fork,  at  an  elevation  of  about  5,300  feet.  Discovered  in 
early  days,  it  was  worked  during  1867  and  1868,  and,  intermittently, 
later.  Some  prospecting  was  done  on  it  in  1896.  It  has  produced  a 
total  of  $500,000.  The  developments  consist  of  a  tunnel  1,400  feet 
long,  and  stopes  above  it.  It  is  a  well-defined  vein,  about  18  inches 
wide,  with  a  northwesterly  strike,  and  carrying  decomposed  quartz 
without  sulphurets.  The  ore  body  was  large  and  the  ore  high  grade, 
containing  up  to  $40  per  ton  in  gold.  The  ore  shoot  was  very  large, 
but  at  a  depth  of  100  feet  it  was  cut  off  by  a  fault  plane  carrying  soft, 
decomposed  granite.  There  are  several  other  veins  in  the  vicinity, 
which,  however,  can  show  no  production. 

The  Summit  vein  is  a  recent  discovery  on  the  ridge  between  Elk 
and  Grimes  creeks,  found  by  tracing  the  placer  gold  of  Deer  Creek 
up  to  its  source.  The  vein  is  inclosed  in  granite,  and  strikes  a  little 
north  of  west,  dipping  45°  SW.  There  is  a  zone,  18  feet  wide,  of 
crushed  granite,  carrying  4  feet  of  pay  ore,  composed  of  the  same 
broken  granite  and  quartz  seams,  and  which  assays  from  $10  to  $40 
per  ton  in  gold.  The  ore  shoot  is  said  to  be  60  feet  long  on  the  sur- 
face. As  usual,  the  vein  carries  much  water  and  is  difficult  ground 
to  timber.  Prospecting  was  in  progress  in  1896,  and  it  was  proposed 
to  sink  a  shaft  400  feet  deep.  Between  the  Summit  vein  and  Center- 
ville  lie,  near  the  road,  two  quartz  claims,  called  the  Golden  Fleece 
and  the  Golden  Star.  A  10-stamp  mill  was  built  long  ago  to  work 
the  ore,  but  the  results  proved  unsatisfactory,  and  the  property  has 
long  been  idle. 

THE  QUARTZBURG-GRIMES  PASS  GOLD  BELT. 

The  whole  lower  drainage  basin  of  Granite  Creek  and  Grimes  Creek 
is  singularly  void  of  gold-quartz  veins.  Three  miles  north  of  Center- 
ville,  at  Crane's  claim,  a  deposit  carrying  much  sulphurets  contain- 
ing gold  and  silver  is  being  prospected.  On  Clear  Creek,  3  miles 
south-southwest  of  Star  Ranch,  at  an  elevation  of  4,475  feet,  are  two 
narrow  quartz  veins  (Jackson's  claim),  inclosed  in  granite  and  carry- 
ing silver  only.  A  small  quantity  of  rich  silver  sulphides  was  found 
18  GEOL,  PT  3 44 


690 


IDAHO    MINING    DISTRICTS. 


on  them,  and  stains  of  copper  and  arsenic  were  noted.     The  strike  is 
north  to  south  and  the  dip  steep  to  the  east. 

Two  and  a  half  miles  southwest  of  Quartzburg  the  gold  belt  begins, 
at  the  Ebenezer  claim.  It  is  not  known  to  extend  west  of  this  point, 
though  gold-quartz  float  has  been  found  2  miles  farther  on,  along 
Dead  Man's  Gulch.  The  direction  of  the  gold  belt  westward  would 
carry  it  directly  to  Horseshoe  Bend,  where  the  Willow  Creek  belt 
begins.  The  high  Boise  Ridge  is  very  brushy  and  difficult  of  explora- 
tion, and  it  is  by  no  means  impossible  that  quartz  veins  will  be  found 
in  the  intervening  stretch. 

TJie  Ebenezer  vein. — This  vein  is  continuous  for  a  distance  of  nearly 
a  mile  across  the  gap  in  the  ridge  between  Canyon  and  Fall  creeks, 
and  three  important  claims  are  located  on  it.  The  Ebenezer  claim 
lies  on  the  Canyon  Creek  side,  and  is  said  to  have  produced  $150,000 
from  sluicing  and  surface  workings.  The  vein  strikes  northeast  and 

southwest  and  dips  to  the 
southeast,  and  is  encased  in 
granite.  It  is  about  5  feet 
wide,  and  consists  of  sheeted 
granite  traversed  by  many 
small  and  rich  quartz  veins. 
The  surface  ore  was  very  rich, 
but  at  a  slight  depth  the  gold 
was  contained  in  sulphides, 
which  did  not  readily  yield 
it  to  simple  amalgamation. 


Scale. 


feet 


has 
last 


FIG.  63.— Section  of  Mountain  Chief  vein,  east  end  of 
claim. 


Only  assessment  work 
been  done  during  the 
years. 

The  Mountain  Chief  ad- 
joins on  the  northeast,  ex- 
tending to  the  summit  of  the  ridge,  at  an  elevation  of  6,000  feet,  and  the 
vein  is  similar  to  the  one  just  described.  It  is  stated  that  10  tons  of  its 
ore  were  milled  in  1895,  yielding  $100  per  ton,  and  much  gold  has  been 
obtained  by  sluicing  the  surface.  Sulphurets  appear  here  also  in 
depth.  In  a  surface  cut  the  section  of  the  vein  was  as  shown  in  fig.  63. 
The  Belzazzar  claim  lies  on  the  Fall  Creek  side  and  has  been  opened 
by  sluicing  and  a  tunnel,  200  feet  below  the  summit.  Bodies  of  heavy 
sulphurets,  chiefly  pyrite,  are  exposed  along  the  vein.  The  western 
part  of  the  vein  lies  in  hornblende-porphyrite,  while  the  eastern  end 
has  granite  in  the  foot  wall  and  the  same  porphyrite  in  the  hanging 
wall. 

A  slightly  divergent  vein,  called  the  Centennial,  lies  a  few  hundred 
feet  southeast  of  the  Mountain  Chief,  on  the  summit  of  the  ridge. 
This  vein  carries  more  silver  than  gold,  and  shows  heavy  iron  pyrite 
in  a  6-inch  seam. 


LINDQBEN.]  QUARTZBURQ-QRIMES   PASS    GOLD    BELT.  691 

The  Gold  Hill  vein. — This  is  probably  the  continuation  of  the 
Ebenezer  vein,  though  it  has  not  been  traced  across  Fall  Creek.  It 
is  continuous  from  the  Newburg,  on  the  divide  between  Fall  Creek 
and  the  west  fork  of  Granite  Creek,  to  at  least  some  distance  east  of 
Quartzburg. 

The  Newburg  claim,  at  an  elevation  of  5,000  feet,  was  worked  exten- 
sively by  surface  sluicing  during  the  early  days,  then  abandoned,  and 
again  located.  It  is  developed  to  some  extent  by  tunnels  aggrega- 
ting several  hundred  feet  in  length.  The  vein  consists  of  a  shattered 
and  decomposed  zone  in  a  belt  of  quartz-porphyrite,  and  reaches  a 
width  of  70  feet.  Narrow  seams  extremely  rich  in  gold  traverse  this 
shattered  zone,  giving  to  the  whole  an  assay  ^lue  variously  stated 
from  $4  to  $12.  The  ore  body  is  evidently  extensive. 

The  Homeward  Bound,  Elizabeth,  and  Mayflower  adjoin  the  New- 
burg  on  the  northeast  across  West  Fork.  Considerable  surface  work 
with  sluices  and  arrastreshas  been  done  on  them.  The  vein  is  about 
5  feet  wide,  and  is  said  to  contain  sulphurets  in  large  quantities  in 
depth.  A  narrow  streak  of  quartz- porphyrite  follows  it.  The  Con- 
federate and  the  Dunlap  adjoin  Gold  Hill  on  the  west,  and  have  a 
strike  of  N.  65°  E.  The  developments  are  not  extensive,  but  some  good 
ore  is  reported  to  occur  on  them.  ' 

The  Gold  Hill  and  Pioneer  claims  constitute  the  most  important 
quartz  mine  in  the  Idaho  Basin,  and  the  only  one  which  has  been 
extensively  and  systematically  worked,  having  been  in  operation  with 
short  interruptions  since  1864.  The  Gold  Hill  was  first  worked  and 
yielded  for  a  long  time  ore  averaging  $20  per  ton.  It  was  first 
exploited  by  tunnels  on  the  northeastern  side  of  Granite  Creek,  but 
in  1875  work  began  below  water  level  in  a  shaft  just  below  Quartz- 
burg  on  the  eastern  branch  of  the  creek,  the  total  depth  attained 
being  400  feet.  In  late  years  the  Gold  Hill  vein  has  been  abandoned 
and  work  concentrated  on  the  Pioneer,  a  claim  adjoining  on  the  south- 
east. The  total  amount  extracted  from  the  Gold  Hill  and  Dunlap 
claims  from  1869  to  1894  is  stated  to  have  been  $1,280,000,  and  the 
production  from  the  Pioneer  claim  from  1884  to  1895  is  stated  to  have 
been  $498,000.  The  total  production  of  the  claims  mentioned,  all  of 
which  was  not  recorded,  is  believed  to  have  been  at  least  $2,225,000. 

In  the  mint  reports  the  following  data  are  found :  Raymond's  report 
for  1872  states  that  Gold  Hill  produced  $300,000  since  September,  1869. 
In  1881  it  is  stated  that  150  tons  of  ore  from  the  Gold  Hill  yielded 
$25,000  in  gold.  In  1883  the  Gold  Hill  produced  $76,800;  in  1884  the 
production  was  $50,000.  The  property  was  equipped  with  a  25-stainp 
mill  in  1875.  No  work  was  in  progress  in  1896,  pending  a  sale  of  the 
mine.  The  Gold  Hill  vein  is  a  well-defined  quartz  vein  with  an  aver- 
age strike  of  N.  70°  E.,  and  a  dip  of  70°  S.  The  foot  wall  is  generally 
sharp  and  well  defined  and  consists  of  granite.  In  the  hanging  wall 
lies  a  dike  of  quartz-porphyrite  several  hundred  feet  wide,  described 


692  IDAHO   MINING   DISTRICTS. 

in  connection  with  dike  rocks  (p.  682).  The  vein  is  of  very  irregular 
width,  from  a  few  inches  up  to  6  feet,  and  has  a  great  tendency  to 
throw  out  stringers  in  the  porphyry  in  the  hanging  wall;  these  when 
followed  were  found  to  be  rich,  but  soon  gave  out.  The  ore  consists 
of  free  gold  and  sulphurets,  the  latter  chiefly  iron  pyrite,  also  some 
antimonite,  which  is  said  to  be  intimately  associated  with  gold.  Small 
traces  of  tellurium  are  also  reported.  About  50  per  cent  of  the  value 
is  in  free  gold,  and  this  proportion  is  likely  to  remain  stable  as  depth 
is  attained.  _  The  sulphurets  are  reported  to  be  of  high  grade.  The 
old  workings  of  Gold  Hill  extend  up  on  the  steep  hill  northeast  of 
Quartzburg. 

The  Pioneer  claim  adjoins  the  Gold  Hill  on  the  south.  A  vertical 
shaft  400  feet  deep  is  sunk  on  it.  It  is  located  on  a  fissured  zone  in 
the  same  porphyry  dike  which  forms  the  hanging  wall  of  Gold  Hill, 
and  which  contains  a  great  number  of  small  seams  with  very  rich  ore, 
the  whole  forming  a  large  body  of  low-grade  ore.  The  porphyry  is 
yellowish  and  decomposed,  filled  with  pyrite,  sericite,  and  some  cal- 
cite.  The  sulphurets  of  the  Pioneer  are  of  much  lower  grade  than 
those  of  Gold  Hill. 

A  short  distance  below  the  Pioneer  there  are  several  claims  on  a 
vein  crossing  the  creek,  the  principal  one  being  called  Mountain  Girl. 
The  ore  consists  chiefly  of  sulphides  without  any  free  gold,  but  some- 
times contains  much  silver,  being  similar  to  the  Centennial,  which 
lies  in  a  similar  position  in  front  of  the  Mountain  Chief  vein. 

Immediately  adjoining  the  Gold  Hill  on  the  northwest  is  a  flat  vein 
called  the  Lone  Star,  from  which,  in  early  days,  much  gold  was 
obtained  by  surface  sluicing. 

The  Iowa  vein. — This  vein  lies  a  short  distance  north  of  the  Gold 
Hill,  and  was  opened  in  1896  by  an  800-foot  tunnel  starting  from  the 
10-stamp  mill  one-eighth  of  a  mile  north  of  Quartzburg.  The  tunnel 
is  driven  through  granite,  which  near  the  vein  is  much  decomposed. 
The  vein  is  a  narrow  seam  in  granite  filled  with  a  soft  clay  gouge  and 
containing  streaks  extremely  rich  in  gold.  There  is  also  some  pyrite. 

In  the  extension  of  the  Iowa  lie  the  Yellow  Jacket  and  other  claims 
which  have  been  less  developed. 

The  Carroll  veins. — A  group  of  five  claims  lies  at  the  head  of  Cali- 
fornia Gulch,  1£  miles  northeast  of  Quartzburg.  The  surface  in  this 
vicinity  was  extremely  rich  and  has  been  extensively  washed.  It 
can  not  be  said  that  the  direction  and  extent  of  the  veins  have  been 
definitely  established,  but  that  rich  veins  exist  in  this  ground  is  not 
to  be  doubted.  On  the  Ivanhoe  claim  some  work  was  done  in  1896, 
the  vein  being  opened  up  by  means  of  a  tunnel  several  hundred  feet 
long  and  exposing  a  good  ore  shoot.  In  this  tunnel  the  vein  dips  south 
at  a  steep  angle,  and  lies  entirely  in  soft,  decomposed  granite.  Outside 
of  the  ore  shoot  the  vein  is  indicated  only  by  a  black-clay  seam.  The 
character  of  the  ore  in  the  shoot  is  illustrated  in  fig.  64,  showing  the 


LINDGREN.] 


QUARTZBURG-GRIMES   PASS   GOLD    BELT. 


693 


breast  of  the  tunnel.  The  valuable  part  consists  of  2  feet  of  decom- 
posed granite  with  seams  3  to  5  inches  wide  of  pyrite.  This  contains 
considerable  free  gold,  some  of  which  appears  to  be  in  the  decomposed 
wall  rock.  Outside  of  the  principal  shoot  there  are  many  streaks  of 
iron  pyrite,  which  do  not  contain  any  free  gold. 

The  Kennebec  claim. — This  property,  situated  one-half  mile  from 
the  Carroll,  yielded  some  very  rich  ground  for  sluicing.  Of  the  vein 
but  little  is  definitely  known. 

Veins  at  head  of  Wolf  Creek. — From  the  Iowa  a  string  of  claims 
extends  through  the  Carroll  and  Kennebec  and  then  farther  through 
the  Black  Bear,  Mountain  Queen,  and  others  up  toward  a  high,  promi- 
nent point  on  the  divide.  All  these  claims  lie  in  granite,  though 
occasional  dikes  cut  the  principal  rocks;  the  main  belt  of  porphyry 
lies  a  little  to  the  south.  On  none  of  them  has  much  work  been 
done.  The  Black  Bear  lies  at  an  ele- 
vation of  5,000  feet  a  short  distance 
to  the  west  of  the  pass  between  Pla- 
cerville  and  Garden  Valley.  The 
strike  is  N.  70°  E.,  and  the  dip  50° 
to  the  south.  The  vein  is  a  well- 
defined  fissure  with  a  pay  streak  of 
good  ore  4  to  5  feet  wide,  which  has 
been  followed  down  for  40  feet.  The 
ore  is  free-milling,  at  present  at  least, 
and  contains  a  little  galena.  North- 
east of  the  pass  lie  a  number  of  more 
or  less  prominent  veins.  The  Gold 
Dollar  is  a  perpendicular  vein,  the 
ore  of  which  carries  no  free  gold,  and 
it  is  said  to  run  from  $2  to  $20  per 
ton.  Near  by  lies  another  vein,  with 
flatter  dip  of  from  20°  to  40°,  carry- 
ing some  free  gold.  The  Monumental 
and  Mountain  Queen  are  on  a  nearly  vertical,  heavy  vein  striking  N. 
81°  E.  It  has  no  distinct  walls,  but  consists  of  streaks  of  quartz  and 
heavy  iron  pyrite  in  decomposed  granite  cut  by  some  porphyry  dikes. 
The  Etna,  lying  a  short  distance  southwest  of  the  pass,  is  said  to 
consist  of  a  streak  in  porphyry  impregnated  with  auriferous  seams 
and  pyrite. 

Veins  in  the  porphyry  dike  east  of  Wolf  Creek. — On  the  summit  1 
mile  east  of  the  pass  is  the  Golden  Chariot,  at  an  elevation  of  5,300 
feet.  The  wide  dike  of  quartz  -  hornblende  -  porphyrite  forms  the 
country  rock.  In  the  tunnel  the  vein  appears  as  a  vertical  streak, 
2  feet  wide,  of  brown  decomposed  rock,  said  to  assay  well.  A  similar 
deposit,  called  the  Buena  Vista,  lies  a  little  to  the  south.  Half  a  mile 
eastward  are  the  Big  Six  and  the  Mineral  Hill  group  of  claims,  in 


•mmm 


FIG.  64.— Breast  of  drift,  Carroll  veins.  To 
the  left,  2  feet  of  altered  granite  with 
rich  seams  of  massive  pyrite;  to  the 
right,  3  feet  of  altered  granite  with 
poorer  seams  of  quartz  and  pyrite. 


694  IDAHO    MINING    DISTRICTS. 

the  same  porphyritic  dike.  The  Big  Six  appears  as  a  brown,  much 
decomposed  vein,  1  to  2  feet  wide,  chiefly  made  up  of  limonite;  it 
strikes  N.  55°  E.  and  dips  steeply  toward  the  northwest,  this  dip  being 
an  unusual  one  for  the  vicinity.  The  claim  is  developed  by  a  small 
shaft,  and  some  fair  assays  were  obtained  from  it,  one  sample  contain- 
ing $10. 33  in  gold  and  $0. 50  in  silver.  The  Mineral  Hill  group  adjoins 
on  the  northeast,  being  situated  on  the  headwaters  of  Ophir  Creek,  at 
an  elevation  of  about  5,000  feet,  and  consists  of  five  claims.  The  sur- 
face is  extremely  decomposed  to  a  brown  loam,  and  luxuriant  vege- 
tation covers  all  outcrops.  These  claims  have  not  yet  been  prospected 
enough  to  determine  their  character,  but  the  pay  appears  to  be  con- 
tained in  streaks  in  the  porphyry,  impregnated  with  pyrite  and  carry- 
ing free  gold  on  the  surface  at  least.  Near  the  Mineral  Hill  claim  a 
large  extent  of  surface  is  said  to  contain  gold.  The  ore  is  a  soft, 
decomposed  rock,  principally  composed  of  limonite,  one  selected  sample 
of  which  assayed  $154  in  gold,  $1.71  in  silver.  Lead  carbonate  also 
occurs  in  the  ore.  Where  sulphurets  are  found  they  are  said  to  be  of 
low  grade.  It  is  probable  that  these  deposits  are  similar  to  that  of 
the  Pioneer  claim,  near  Quartzburg. 

Claims  near  Grimes  Pass. — For  3  miles  beyond  the  Mineral  Hill 
group,  in  a  northeasterly  direction,  no  mineral  deposits  are  known, 
though  the  deep  soil  covering  the  region  makes  it  probable  that  no 
thorough  prospecting  has  ever  been  undertaken.  About  three-fourths 
mile. west  of  Grimes  Pass,  on  the  summit  of  the  ridge  dividing  the 
waters  of  the  Payette  and  Boise  rivers,  at  an  elevation  of  5, 000  feet, 
lie  a  number  of  claims  called  the  Morning  Star  group.  There  are 
eight  claims  laid  out  along  two  adjoining  lines.  The  deep  surface 
soil  makes  prospecting  difficult,  and  the  exact  character  of  the  deposit 
is  not  known.  Over  a  large  extent  the  surface  gives  good  prospects, 
and  many  little  shafts  demonstrate  the  presence  of  a  considerable 
body  of  low-grade  free-milling  ore.  The  ore  has  always  the  appear- 
ance of  streaks,  4  to  6  feet  wide,  of  decomposed  and  brownish  por- 
phyry, striking  a  trifle  north  of  east.  The  deposits  lie  in  a  dike, 
several  hundred  feet  wide,  of  quartz-hornblende-porphyrite,  continu- 
ing from  the  vicinity  of  Quartzburg,  but  the  contacts  of  the  dike  with 
the  granite  are  difficult  to  trace.  Samples  of  the  ore  washed  in  pan 
gave  good  prospects  of  free  gold,  with  some  lead  carbonate.  On  the 
Morning  Star  a  shaft  232  feet  deep  has  been  sunk.  A  long  tunnel 
has  been  started  on  the  Payette  side,  600  feet  vertically  below  the 
shaft,  and  is  calculated  to  strike  the  vein  1,700  feet  from  the  mouth. 
In  1896  it  had  been  driven  as  far  as  a  point  vertically  below  the  shaft, 
but  work  had  to  be  suspended  on  account  of  financial  difficulties. 
Three  hundred  feet  back  from  a  point  perpendicularly  below  the 
shaft  the  contact  of  granite  and  porphyry  was  struck  in  the  tunnel. 
The  deposits  are  evidently  similar  to  those  of  the  Pioneer  mine  and 
the  Mineral  Hill  group,  and  consist  of  a  more  or  less  shattered  zone 


LINDGEEN.]  MINING   DISTRICTS   EAST    OF   THE   BASIN.  695 

in  porphyry,  which  has  been  impregnated  with  auriferous  sulphides 
by  thermal  action.  The  ore  will  probably  be  base  in  depth,  but  near 
the  surface  a  considerable  amount  of  free-milling  ore  exists. 

The  Mountain  Queen  mine  lies  on  Grimes  Creek,  3  miles  above  the 
Pioneer,  at  the  southern  edge  of  the  porphyry  dike  and  about  one- 
fourth  mile  from  the  Morning  Star  claims.  It  is  probably  not  the 
extension  of  the  latter,  but  a  more  southerly  vein.  A  few  years  ago 
a  20-stamp  mill,  driven  by  water  power,  was  constructed  on  this  prop- 
erty .and  ran  two  years.  At  first  the  ore  is  said  to  have  been  taken 
from  a  well-defined  quartz  vein,  but  later  the  mineralized  porphyry 
was  mined  and  milled  and  was  found  too  poor  for  profitable  work. 

The  porphyry  dike  extends  eastward  toward  the  high  hills  east  of 
Grimes  Pass,  but  was  not  followed  and  examined  any  farther.  At 
Charlotte  Gulch,  on  the  east  side  of  Grimes  Pass,  are  many  claims 
which  on  the  decomposed  surface  carried  much  free  gold.  The 
veins  contain  pyrite,  galena,  and  blende,  with  a  small  amount  of  free 
gold.  Mr.  Woods,  of  Placerville,  states  that  there  is  evidence  that 
those  veins  have  been  much  disturbed  by  faulting. 

MININ&  DISTRICTS  EAST   OF  THE  BASIN. 

The  Summit  Flat  mining  district  lies  on  the  headwaters  of  Elk 
Creek,  Clear  Creek,  and  Moore  Creek,  at  elevations  of  from  6,000  to 
8,000  feet,  and  12  miles  north-northeast  of  Idaho  City.  At  the  head- 
waters of  Elk  Creek  are  the  Barry,  Peerless,  King,  and  other  veins, 
while  the  Wilson  group  of  claims  lie  a  little  farther  north.  The  veins 
generally  strike  east  to  west,  or  a  little  north  of  east,  and  dip  south 
at  steep  angles.  In  character  they  are  apparently  well-defined,  wide 
fissure  veins  carrying  much  quartz,  chiefly  free  milling,  though 
bunches  of  sulphurets  may  occur.  The  Mammoth  claim  in  the 
Wilson  group  is  opened  by  means  of  an  incline  325  feet  deep,  expos- 
ing a  considerable  body  of  ore.  There  are  two  small  mills  in  this 
mining  district.  This  region  was  not  visited  by  the  writer  in  1896. 

Between  Summit  Flat  and  Kempner,  10  miles  to  the  east,  are  many 
prospects  with  only  slight  developments,  partly  carrying  gold  ores, 
partly  silver  ores.  Placer  deposits  occur  at  many  places  along  Lost 
River  and  Bear  River  near  Kempner.  Twenty-two  miles  northeast 
of  Idaho  City  the  silver  mines  of  Banner  are  located,  which  produced 
considerably  before  the  recent  fall  in  price  of  silver.  Between  1882 
and  1894  the  total  silver  production  of  this  district  probably 
amounted  to  $1,500,000  or  12,000,000,  reaching  a  maximum  of  over 
$200,000  in  1892.  At  present  these  mines  are  shut  down.  The 
deposits  are  large,  well-defined  quartz  veins  carrying  rich  silver 
sulphides. 

Gold-quartz  veins  have  been  found  on  the  southwestern  slope  of 
Sunset  Mountain,  and  several  claims  have  lately  been  located  on 


696 


IDAHO    MINING    DISTRICTS. 


upper   Rabbit    Creek,   draining  into   Boise   River  8    miles  east  of 
Idaho  City. 

Fineness  of  quartz  gold. 


Mine. 

Value  per  ounce. 

Fineness. 

G-ambrinus           

$15.  50 

Boulder  

15.  50-16.  00 

680  to  718 

Forest  King            

700 

Washington                 

15.00 

Illinois                    ..  

15.00 

Ebenezer 

16.50 

Gold  Hill      

a  17.  50 

800  to  910 

a  Average. 
THE    GEOLOGICAL    HISTORY    OF    THE    IDAHO    BASIN. 

The  succession  of  geological  events  to  which  the  existence  of  the 
basin  and  of  the  gold-bearing  gravels  is  due  is  neither  simple  nor  easy 
to  decipher.  In  a  large  degree  this  is  owing  to  the  very  monotonous 
structure  of  the  bed-rock  series,  which  gives  few  clews,  except  those 
indicated  by  the  topography,  to  the  character  of  the  movements  that 
have  taken  place,  for  it  soon  becomes  apparent,  during  a  study  of  the 
district,  that  erosion  alone,  unaided  by  orographic  movements,  can 
not  have  produced  this  peculiar  depression  situated  on  the  divide 
between  two  main  rivers. 

The  doubtful  age  of  the  granite,  which  alone  constitutes  nearly  the 
whole  pre-Tertiary  series  in  the  basin,  has  already  been  alluded  to. 
It  has  further  been  stated  that  a  surface  laid  through  the  ridge  lines 
of  the  Boise  Mountains  in  general  probably  forms  part  of  an  old  pre- 
Tertiary  peneplain  or  land  mass  planed  down  by  erosion;  and,  still 
further,  that  the  erosion  succeeding  the  uplift  which  differentiated 
the  Boise  Mountains  and  the  Snake  River  plains  had,  prior  to  the 
lake  period,  cut  far  into  this  uplifted  surface,  so  far,  indeed,  that 
the  Boise  Canyon  at  its  mouth  was  cut  to  its  present  depth  at  the 
beginning  of  the  Neocene.  All  this  does  not  account  for  the  depres- 
sion of  the  basin,  which  lies  much  below  the  general  level  of  that 
surface.  It  seems  probable  that  the  present  upper  valleys  of  Grimes 
and  Moore  creeks  have  been  excavated  by  erosion,  but  this  again 
does  not  account  for  the  basin  as  a  whole.  In  it  the  river  valleys 
are  separated  by  low  ridges,  the  summits  of  which  form,  if  extended, 
an  undulating  surface  considerably  above  the  creeks,  it  is  true,  but 
still  much  below  the  general  surface  of  the  surrounding  country,  as 
is  well  shown  by  PI.  XCI.  The  extent  of  this  surface  determined 
the  existence  of  the  basin  in  the  first  place,  and  as  a  probable  work- 
ing hypothesis  to  account  for  this  it  may  be  assumed  that  this  earlier 


LINDGREN.]         GEOLOGICAL    HISTORY    OP    THE    IDAHO    BASIN.  697 

basin  was  caused  by  a  sinking  of  a  portion  of  the  Boise  Mountains 
along  curved  fault  lines  between  the  Boise  Ridge  on  the  west,  Wilson 
Peak  and  other  elevations  on  the  east,  and  the  Thorn  Creek  Hills  on 
the  south.  The  age  of  the  quartz  veins  in  the  basin  can  not  be  defi- 
nitely indicated,  but  is  most  likely  Cretaceous  or  Eocene.  They 
were  certainly  formed  before  the  deposition  of  the  Payette  lake  beds, 
and  it  is  to  be  expected  that  the  rivers  and  creeks  of  the  pre-Payette 
period  of  erosion  in  the  basin  carried  detrital  gold  derived  from 
these  veins.  These  stream  gravels  are  now  either  completely  eroded 
or  buried  below  the  lake  beds  at  Idaho  City.  As  has  been  ex- 
plained in  the  detailed  description,  there  is  slight  chance  of  finding 
them  by  boring,  and  still  slighter  chance  of  mining  them  profitably 
if  found. 

The  surface  of  the  Payette  lake  attained  a  height  above  the  present 
sea  level  of  4,200  feet  at  the  mouth  of  the  Boise  Canyon.  If  the  eleva- 
tions and  the  topography  were  then  the  same  as  at  the  present  time, 
the  lake  would  have  reached  up  as  far  as  Centerville  in  Grimes  Creek, 
and  4  miles  above  Idaho  City  in  Moore  Creek.  It  is  almost  certain, 
however,  that  the  relative  elevations  are  not  the  same,  for  near  Idaho 
City  we  find  the  Payette  lake  beds  at  4,400  feet,  and  there  forming 
part  of  a  smaller  area  which  has  settled  down  between  parallel  fault 
lines— just  how  much  is  not  known.  From  this  it  appears  that  the 
basin  has  increased  its  elevation  somewhat  relatively  to  the  country 
at  the  mouth  of  the  Boise  Canyon.  High  up  near  the  divide,  on  Muddy 
Creek,  a  small  remnant  of  inclined  lake  beds  occurs,  but  it  is  perhaps 
a  small  local  accumulation.  At  any  rate  it  is  certain  that  the  Payette 
lake  covered  the  lower  part  of  the  basin  in  early  Neocene  times. 

The  lake  beds  were  rapidly  accumulated  in  the  bay  then  occupying 
the  basin,  and  as  no  concentration  of  the  material  took  place,  it  was 
natural  that  their  content  of  native  gold  should  be  very  slight. 

The  raising  of  the  base  level  to  the  present  elevation  of  over  4,000 
feet  would  naturally  produce  extensive  accumulations  of  gravel  in 
the  creeks  draining  to  the  lake.  It  is  probable,  indeed,  that  at  this 
time  of  maximum  lake  extension  the  lower  valleys  opening  into  the 
basin  were  choked  with  gravel;  and  as  an  evidence  of  this  may  be 
cited  the  occurrence  of  auriferous  river  gravel  on  the  summit  of  a 
ridge  in  the  Thorn  Creek  drainage,  at  an  elevation  of  4,500  feet. 
Vast  eruptions  of  basic  lavas  took  place  on  the  summit  and  western 
side  of  the  Boise  Ridge,  and  to  less  extent  in  the  basin.  All  of  these 
earlier  lavas  probably  flowed  out  during  the  deposition  of  the  lake 
beds.  As  the  lake  receded  stream  courses  were  established  over  its 
deposits,  and  the  streams  which  headed  near  quartz  veins  began  to 
carry  down  their  precious  load  and  concentrate  the  gold  on  the  bed 
rock.  These  fluviatile  deposits,  which  were  formed  very  shortly  after 
the  Payette  lake  beds,  or  perhaps  in  part  contemporaneously  with 
them  in  valleys  draining  into  the  lake,  have  been  described  as  "older 


698  IDAHO    MINING   DISTRICTS. 

gravels."  Among  them  are  the  deposits  of  Gold  Hill,  East  Hill,  and 
Barker's  claim  at  Idaho  City,  as  well  as  the  Ranch  Company's  claims 
and  other  gravels  near  Placerville.  They  rest  partly  on  the  lake 
beds,  partly  on  granite;  and  while  these  gravels  at  Idaho  City  may 
have  been  deposited  by  Moore  Creek  as  very  high  bench  gravels,  the 
gravels  at  Placerville  form  a  part  of  a  drainage  system  differing  from 
the  present  one. 

During  the  period  of  general  erosion  following  the  retreat  of  the 
Payette  lake  important  events  took  place.  The  lower  canyon  of 
Moore  Creek  was  scoured  of  its  accumulated  gravels.  The  lake  beds 
were  disturbed  and  acquired  a  decided  dip  to  the  west.  One  block 
of  them  at  Idaho  City  sunk  down  between  fault  lines,  being  thus  pre- 
served from  the  erosion  which  destroyed  the  larger  part  of  them.- 
The  gravels  laid  down  on  the  lake  beds  also  show  a  tilting  westward, 
though  at  slighter  angles  than  the  latter.  Near  Placerville  and 
Granite  there  were  extensive  disturbances,  which  greatly  changed 
the  old  drainage.  Along  the  eastern  side  of  the  Boise  Ridge  these 
disturbances,  it  would  .appear,  took  the  form  'chiefly  of  faulting,  for 
along  this  line  the  old  gravels  are  cut  off;  but  the  amount  of  this 
faulting  is  not  easy  to  establish.  In  this  connection  the  occurrence 
of  a  little  gravel  on  the  summit  of  the  Boise  Range  is  of  great  inter- 
est, and  it  is  difficult  to  explain..  It  is  not  believed,  however,  that 
the  disturbance  was  so  great  as  to  create  the  whole  of  this  ridge  at 
this  time. 

Finally,  at  the  close  of  the  Pliocene  came  the  eruption  of  the  Snake 
River  basalts.  The  Moore  Creek  flow  originated  at  some  point  on 
Grimes  Creek  a  few  miles  below  the  basin,  and  as  it  dammed  the 
stream  to  an  elevation  of  100  feet  the  natural  result  was  the  accumu- 
lation of  bench  gravels  above  by  the  checking  of  erosion.  As  the 
creek  gradually  wore  through  the  basalt  filling,  the  level  at  which 
bench  gravels  were  formed  gradually  sunk.  Thus  the  bench  gravels, 
lining  the  stream  up  to  100  feet  above  their  beds,  are  directly  due  to 
the  Pliocene  basaltic  eruption,  and  represent  in  the  basin  the  deposit 
of  the  Pleistocene  times. 


CHAPTER    V. 
THE  MINING  DISTRICTS   OF  THE  BOISE  RIDGE. 

NEAL    MINING    DISTRICT. 
LOCATION. 

The  Neal  mining  district  is  situated  south  of  the  Boise  River,  just 
east  of  Three  Point  Mountain,  on  the  head  of  Wood  Creek,  in  Elmore 
County,  15  miles  southeast  of  Boise,  in  the  southwest  corner  of  the 
Idaho  Basin  quadrangle. 

The  district  embraces  about  10  square  miles,  but  the  productive  area 
has  been  confined  to  the  heads  of  Wood  and  Bender  creeks.  The  camp 
was  discovered  in  1889,  and  has  been  worked  since  during  the  summer 
months,  producing  about  $200,000  in  gold.  Three  mills  have  been 
erected,  a  10-stamp  for  the  Homestake,  probably  the  oldest  mill  in  the 
State,  having  been  first  used  in  Idaho  Basin;  a  5-stamp  for  the  Alice 
mine,  now  a  custom  mill ;  and  a  10-stamp  for  the  Lilly  mine  on  Black 
Creek,  now  idle. 

Placer  mining  has  been  confined  to  a  few  bars  and  the  creek  beds, 
but  the  product  from  this  source  forms  a  very  inconsiderable  part  of 
the  camp's  output.  The  largest  amount  extracted  from  the  placers  is 
said  to  have  been  $800. 

The  western  half  of  the  district  is  bare  of  timber,  and  except  in  the 
main  streams  there  is  during  the  summer  months  a  scarcity  of  water. 
The  eastern  half  is  better  timbered. 

PI.  XCVII,  drawn  by  Mr.  F.  D.  Howe,  shows  the  topography, 
dikes,  veins,  and  mining  claims  of  the  central  part  of  the  district. 

TOPOGRAPHY. 

The  main  topographic  feature  is  the  high  ridge  which,  with  a 
WNW.-ESE.  trend,  divides  the  Snake  River  from  the  South  Fork  of 
the  Boise,  and  which  only  reaches  an  elevation  of  about  5,000  feet. 
At  Three  Point  Mountain  this  ridge  swings  to  a  northerly  direction, 
and  culminates  4  miles  farther  north  in  a  point  5,400  feet  high, 
between  Birch  and  Grouse  creeks,  overlooking  the  mouth  of  Moore 
Creek  and  the  forks  of  the  Boise  River.  A  number  of  deep  canyons 
separated  by  narrow  ridges  radiate  from  the  vicinity  of  Three  Point 
Mountain.  To  the  southwest  extend,  at  the  foot  of  Three  Point  Moun- 
tain, the  Tertiary  formations  of  the  Snake  River  Valley.  The  direc- 
tion of  the  creeks  seem,  in  some  measure,  to  follow  the  lines  of  faults 
and  jointing — that  is,  they  extend  from  north-northwest  to  south- 
southeast  and  from  east  to  west. 

699 


700  IDAHO    MINING    DISTRICTS. 


GEOLOGY. 

The  prevailing  rock  is  the  normal  gray  granite  of  the  Boise  Moun- 
tains, composed  of  orthoclase,  plagioclase,  quartz,  and  biotite ;  horn- 
blende is  of  rare  occurrence  in  it.  A  jointed  structure  or  sheeting  is 
often  noted,  the  direction  (N.  50°  to  80°  E.)  and  dip  (up  to  45°  S.) 
roughly  corresponding  to  those  of  the  veins.  Numerous  dikes  cut  the 
granite,  and  may  be  divided  into  several  classes. 

Some  of  the  dikes  consist  of  a  harder  gray  granite,  which  carries 
some  muscovite.  Less  frequent  are  dikes  of  coarser  and  more  mica- 
ceous character  than  the  general  mass.  Along  the  north  side  of  Wood 
Creek  are  several  dikes  of  a  pyritiferous  granite,  occurring  at  one 
place  as  foot  wall  to  a  vein. 

The  most  prominent  dikes  are  those  which  crop  so  boldly  on  Black 
Creek,  about  3  miles  southwest  of  the  Homestake  mine,  and  which, 
according  to  Mr.  Howe,  continue  for  a  long  distance  northward  with 
a  general  trend  of  N.  5°  W.,  one  of  them,  the  most  easterly,  showing 
on  the  map  Their  width  is  up  to  200  feet.  The  rock,  which  has  a 
somewhat  porous  character,  is  dark  gray  in  color  with  brownish  spots; 
phenocrysts  of  feldspar  are  abundant,  and  are  usually  about  5mm  long. 
It  is  almost  impossible  to  obtain  fresh  rock.  The  microscope  shows 
the  rock  to  consist  of  sanidine  phenocrysts;  small,  brownish,  decom- 
posed foils  and  prisms,  probably  decomposed  biotite;  and  a  holocrys- 
talline  groundmass,  of  spherulitic  and  micropegmatitic  character,  of 
orthoclase  and  some  quartz.  The  rock  should  probably  be  classed  as 
a  syenite-porphyry. 

Normal  granite-porphyry  is  common  and  forms  dikes,  more  rarely 
irregular  masses,  with  a  general  direction  of  N".  20°  to  30°  W. ,  several 
occurring  on  the  divide  between  Wood  and  Grouse  creeks. 

Lastly,  there  are  narrow  dikes  of  lamprophyres,  dark-green,  dense 
rock,  in  which  small  foils  of  black  mica  are  often  seen.  These  vary 
from  18  to  30  inches  in  width  and  often  trend  with  the  vein  N.  78°  E. 

A  specimen  of  thislamprophyric  dike  rock  from  the  Hidden  Treasure 
mine  is  a  panidiomorphic  granular  rock  composed  of  brown  horn- 
blende, augite,  and  soda-lime  feldspar  in  slender,  lath-like  forms; 
probably  also  some  orthoclase.  The  rock  is  very  similar  to  certain 
camptonites,  or,  perhaps,  stands  between  a  minette  and  a  camptonite. 
Similar  dikes  also  occur  in  the  Homestake  mine,  and  in  the  foot  wall 
of  the  High  Five  is  a  dike  15  feet  thick,  of  lamprophyric  rock  with 
abundant  black  mica  and  porphyritic  orthoclase  crystals.  These 
dikes  are  sometimes  the  hanging  wall  of  the  veins,  at  times  appar- 
ently not  affected  by  the  vein  processes,  at  others  partially  or  entirely 
replaced  by  ore.  At  one  place  in  the  Homestake  mine  a  part  of  this 
dike,  crushed  and  altered,  lies  in  the  middle  of  a  4-foot  vein.  Mr. 
Howe  concludes  from  his  observations  that  the  lamprophyres  are  the 
oldest  dikes,  followed  by  the  large  dikes  of  syenite-porphyry,  and 


LINDGRKN.] 


VEINS    OF    NEAL   MINING    DISTRICT. 


701 


these  again  by  the  granite-porphyry.  It  is  probable  that  all  of  them 
antedate  the  veins.  Remains  of  a  glassy  rhyolite  are  found  on  Three 
Point  Mountain  and  the  ridges  northward. 

THE  VEINS. 


The  Neal  district  was  visited  in  October,  1896,  but  only  two  days 
could  be  devoted  to  it,  and  I  therefore  gladly  availed  myself  of  the 
offer  of  the  following  notes  by  Mr.  F.  D.  Howe,  superintendent  of 
the  Hidden  Treasure  mine,  who  is  thoroughly  familiar  with  the  dis- 
trict and  with  whose  statements  my  own  observations  in  the  principal 
mines  fully  agree.  Credit  for  many  of  the  above  data  regarding  the 
dikes  of  the  district  is  also  due  to  Mr.  Howe. 

The  veins  of  the  district  have  the  common  N.  70°  to  83°  E.  trend  and  the  same 
general  dip  to  the  south,  and  for  form  may  be  referred  to  three  classes:  First,  veins 
filling  larger  fault  fissures,  on  which  are  located  the  principal  mines;  second,  veins 
along  the  minor  shearing  planes  of  the  granite,  more  or  less  irregular,  but  gen- 
erally carrying  high-grade 
ore;  and  third,  veins  of  a 
hard  white  quartz,  called  by 
the  miners  "bull  quartz," 
carrying  no  values. 

The  veins  on  the  fault 
fissures  are  often  displaced 
by  faults  of  a  north-south 
trend,  which  occurred  sub- 
seqtient  to  the  vein  filling. 
The  position  of  the  north- 
south  faults  is  often  shown 
on  the  surface  by  gulches  of 
greater  or  less  size.  The  dip  FIG.  65.— Cross  section  of  vein  in  the  Neal  mining  district, 
is  to  the  south,  ranging  from 

30°  to  54°,  somewhat  steeper  than  that  of  the  foliation.  The  granite  of  the  foot 
wall  for  some  little  distance  away  from  the  vein  has  suffered  a  decomposition  of 
its  mica,  is  harder,  and  is  cut  by  cross  jointing  planes,  in  which  are  thin  seams 
of  a  talcose  mineral,  giving  it  a  blocky  appearance.  Garnets  occur  on  this  side  of 
the  fissure  and  may  be  of  secondary  origin.  On  the  hanging- wall  side  the  granite 
is  darker,  and  the  main  joints  follow  the  fissure  and  no  cross  jointing  appears. 
On  this  side  only  appear  the  oxides  of  manganese.  Beyond  the  sheeting  or  joint- 
ing of  this  side  there  is  a  zone  of  structureless  granite  (fig.  65). 

The  vein  filling  is  separated  from  the  walls  by  thin  seams,  but  in  places  the 
mineralization  extends  into  both  walls,  in  which  case  the  gold  in  the  walls  is 
coarser  than  that  of  the  vein  proper. 

The  vein  matter  consists  of  quartz,  sulphides,  and  partly  replaced  country  rock. 
The  ordinary  structure  is,  next  the  hanging  wall,  a  clear  quartz,  more  or  less 
honeycombed  and  stained  by  the  oxidation  of  the  iron  pyrites;  next,  a  zone  of 
replaced  country  rock,  granite  or  one  of  the  dark  rocks  described  above,  carry- 
ing much  pyrite  and  other  sulphides. 

Pyrite  often  occurs  in  the  dike  rock  in  detached  kidneys  and  sometimes  as  par- 
tial replacements.  The  width  of  the  veins  varies  from  2  to  13  feet.  The  gold 
occurs  free  in  the  quartz;  partially  free  in  the  pyrites.  It  varies  from  microscopic 


702  IDAHO   MINING   DISTRICTS. 

to  shot  size,  and  in  some  of  the  very  rich  pockets  the  oxidation  of  the  pyrites  has 
left  a  semicrystalline  form.  It  is  worth  $15  per  ounce  from  the  retort,  the  alloy 
being  silver.  The  associated  sulphides  are  iron  pyrites  and  galena,  and  a  little 
zinc  blende  appearing  on  the  surface  as  iron  oxides  and  cerussite.  From  the 
pure  galena  silver  values  as  high  as  160  ounces  per  ton  have  been  obtained,  one 
assay  showing  0.7  ounce  of  gold  and  44  ounces  of  silver.  The  pyrites  contain  as 
high  as  21  ounces  of  gold  per  ton.  An  assay  of  clean  zincblende  contained  1.4 
ounces  of  gold  per  ton.  The  pyrites  constitute  from  3  to  10  per  cent  of  the  ore 
as  broken;  the  galena  less  than  1  per  cent.  From  40  to  65  per  cent  of  the  gold 
is  saved  by  amalgamation.  The  values  of  the  milled  ore  range  from  $10  to  $120 
in  gold  per  ton,  the  larger  part  being  between  $10  and  $35.  Concentrates  carry 
about  2.5  to  4  ounces  in  gold  and  5  to  6  ounces  in  silver  per  ton. 

The  veins  of  the  second  class  have  less  development',  and  with  two  or  three 
exceptions  have  produced  but  little  ore.  They  occur  nearly  parallel  to  the  fissures 
at  some  distance  on  either  side,  and  differ  in  having  less  dip,  little  or  no  complete 
replacement  of  the  country  rock,  and  less  regularity  to  the  ore  bodies.  Generally 
the  values  are  high.  Where  they  have  been  productive  the  veins  occur  along  the 
line  of  dike  contacts,  as  at  the  High  Five  and  Golden  Star.  The  foot  wall  is  here 
a  granitic  porphyry  and  apparently  lies  parallel  with  the  jointing  or  sheeting. 

The  veins  of  the  third  class  are  the  most  prominent  in  the  way  of  outcropping, 
the  hard  white  quartz  having  suffered  but  little  from  surface  decomposition. 
Occasionally  the  quartz  is  heavily  stained  by  the  iron  oxides,  and  in  places  scat- 
tering pyrites  are  found,  but  the  values  are  low.  In  places  along  the  sides  of  this 
"bull  quartz  "  have  been  found  streaks  of  high-grade  ore,  but  there  has  been  no 
development  to  determine  whether  the  hard  quartz  caps  softer  ore,  as  it  does  in 
other  parts  of  the  State. 

Several  prospects  are  found  northwest  of  Three  Point  Mountain,  in  Charcoal 
Ravine.  The  main  developments  have  been  on  the  Jackson  property — a  narrow 
dike,  8  to  12  feet,  of  quartz-porphyry,  with  quartz  veins  on  the  joint  and  contact 
surfaces.  The  quartz  carries  a  coarse  gold,  and  there  is  some  impregnation  of  the 
porphyry  mass. 

In  the  central  belt  the  principal  vein  is  the  Homestake-Hidden  Treasure.  On  the 
Homestake  claim  one  shoot  of  ore,  varying  in  length  from  75  to  125  feet  and  in 
width  from  4  to  12  feet,  has  been  mined  through  tunnels  to  a  depth  of  350  feet. 
To  the  west  the  vein  is  cut  by  a  fault,  striking  N.  19°  W.  and  dipping  60°  E. 
Beyond  this  fault  the  vein  was  recently  found  again,  thrown  100  feet  to  the  south. 
Four  hundred  feet  to  the  east,  in  which  distance  another  shoot  is  opened,  a  section 
of  the  vein  is  faulted  200  feet  to  the  north.  This  faulted  section  is  another  ore 
shoot,  and  is  about  250  long.  Beyond  this,  to  the  east,  another  shoot  has  been 
mined  to  a  depth  of  100  feet.  The  term  "ore  shoot"  refers  only  to  ores  yielding 
$10  per  ton  and  over;  if  made  to  include  ores  from  $5  per  ton  and  up,  the  vein  so 
far  as  opened  is  practically  one  shoot.  The  greatest  depth  attained  below  the 
surface  is  350  feet. 

On  the  Hidden  Treasure,  the  easterly  extension  of  the  Homestake,  the  vein  has 
been  opened  for  450  feet,  to  a  depth  of  165  feet,  varying  in  width  from  1  to  13  feet. 
Several  small  displacements  by  north-south  faults,  between  4  and  12  feet,  are 
shown,  and  one  with  a  displacement  of  60  feet.  The  entire  top  of  the  vein  has 
been  moved  to  the  south  on  a  fault  plane  dipping  6°  or  8°  to  the  northeast,  between 
60  and  100  feet.  In  one  place  this  plane  was  filled  with  ore.  About  90  per  cent  of 
the  production  of  the  camp  has  been  from  these  two  properties. 

In  the  High  Five  and  the  Golden  Star  a  vein  has  been  opened,  with  the  granitic 
porphyry  for  a  f  oo twall.  It  apparently  dips  with  the  foliation.  The  high-grade 
ores  occur  in  lenticular  masses  of  greater  or  less  extent.  The  value  or  extent  of 
the  rest  of  the  vein  material  has  not  been  determined. 


LINDOREN.]  VEINS    OF    NEAL    MINING    DISTRICT.  703 

The  vein  is  in  width  from  2  to  6  feet,  and  in  form  and  character  of  ores  is  bnt 
little  different  from  the  Homestake  vein. 

On  the  Corder  property  (Sunshine)  an  ore  shoot  has  been  developed  on  a  fault 
fissure,  with  the  ordinary  dip  and  trend;  and  120  feet  to  the  north  a  parallel  vein, 
dipping  30°  to  the  north,  has  been  opened.  Each  vein  averages  4  feet,  and  the 
ores  are  similar  in  character  and  value  to  the  type  ores  of  the  camp. 

On  Indian  Creek,  5i-  miles  southeast  of  Neal,  a  vein  has  been  opened  on  the 
Stevens  and  Beck  properties  for  6,000  feet  along  its  trend.  It  is  a  fault  fissure  4 
to  8  feet  wide  and  carries  ores  similar  in  character  and  value  to  those  of  Neal. 

On  Black  Creek,  4  miles  southwest  of  Neal,  several  veins  have  been  opened  and 
some  little  production  made.  Work  on  them  has  been  done  only  at  odd  times. 
The  values  are  high  and  the  limited  developments  indicate  strong  veins. 

Two  miles  east,  along  Wood  Creek,  are  two  recent  developments,  the  North 
Star  and  the  Clements  mines,  both  being  of  the  common  type  of  the  district.  In 
the  first  named  arsenopyrite  occurs. 

Milling  charges  have  been  $5  per  ton;  transportation,  from  $1  up,  and  the  mill 
saving  not  over  55  per  cent — that  is,  only  the  free  gold — thus  requiring  §12  to  $15 
ore  to  pay  the  outside  expenses  only.  To  the  smelter  the  charges  aggregate  $28  to 
$35  per  ton.  It  would  be  safe  to  say  that  nothing  less  than  $25  rock  would  return 
more  than  wages  to  the  owner  unless  he  had  a  mill.  The  average  claim  owner 
had  either  to  make  the  claim  pay  or  limit  the  development  to  the  annual  assess- 
ment, carelessly  done.  The  work  in  the  camp  is  a  result  of  this  condition  and 
fully  illustrates  it. 

To  these  full  notes  of  Mr.  Howe  should  be  added  only  the  statement 
that  the  alteration  of  the  country  rock  adjoining  the  veins  is  of  the 
same  character  as  that  at  other  places  within  the  region  described. 
The  black  mica  is  bleached,  being  converted  to  carbonates  and  to 
white  mica.  The  feldspars  are  converted  to  an  opaque  white  matter, 
which  is  neither  kaolin  nor  talc,  but  sericite  in  extremely  fine-grained 
aggregates.  The  quartz  grains  remain  unaltered  in  general,  and 
pyrite  and  arsenopyrite  are  often  introduced.  The  principal  value 
of  the  veins  is  in  the  filling — that  is,  in  the  solid  quartz  accompanied 
by  sulphides.  But  the  altered  granite  next  the  filling  here  sometimes 
also  carries  good  value. 

BLACK    HORNET    MINING    DISTRICT. 
TOPOGRAPHY. 

This  district  and  its  continuation  northward  (the  Deer  Creek  min- 
ing district)  is  on  the  eastern  side  of  the  Boise  Ridge,  on  the  slope  of 
the  ridge  culminating  in  Lucky  Peak.  It  is  8  miles  east-southeast 
of  Boise,  and  is  situated  at  elevations  ranging  from  4,500  to  5,500 
feet.  The  topography  is  very  accentuated;  deep,  sharply  incised 
V-shaped  canyons  score  the  slope  of  the  Lucky  Peak,  draining  to 
Boise  River  and  to  Moore  Creek.  'Scattered  timber  covers  the  hill- 
sides at  higher  elevations.  The  topography  is  indicated  in  a  some- 
what generalized  way  on  the  Boise  sheet. 


704  IDAHO    MINING    DISTRICTS. 

GEOLOGY. 

The  geological  structure  of  the  Lucky  Peak  ridge  is  very  simple. 
It  consists  nearly  entirely  of  the  normal  granite  of  the  Boise  Moun- 
tains. A  number  of  dikes  vary  the  monotony,  but  consist  almost 
exclusively  of  light-colored  granite-porphyry,  which  have  in  general 
a  northwesterly  trend  and  a  width  occasionally  attaining  100  feet,  but 
usually  much  less.  Placer  deposits  hardly  found  place  to  accumulate 
in  the  steep  gulches  and  cut  no  figure  in  the  production  of  the  camp, 

MINERAL,  DEPOSITS. 

A  number  of  gold-quartz  veins  are  found  in  the  Black  Hornet  dis- 
trict; and  they  are  not  confined  to  the  district.  Scattered  small  veins 
occur  in  the  granite  between  this  region  and  the  Neal  mining  district, 
9  miles  to  the  southeast.  West  and  southwest  from  Lucky  Peak  scat- 
tered prospects  are  also  found;  likewise  to  the  north  and  northwest, 
connecting  in  the  latter  two  directions  with  the  Shaw  Mountain  and 
the  Boise  districts.  The  northern  part,  or  the  Deer  Creek  district, 
has  been  known  for  a  long  time.  On  the  Montana  claim  an  arrastre 
was  built  and  worked  many  years  ago  by  Mr.  Plowman,  of  Idaho  City. 
But  the  southern  and  lately  most  productive  part,  near  the  Black 
Hornet  mine,  has  been  known  only  during  the  last  few  years. 

The  production  has  been  confined  almost  entirely  to  ore  shipped  to 
smelting  works  from  the  Black  Hornet  or  Ironsides  mine.  During 
1895  and  1896,  200  carloads  are  said  to  have  been  shipped,  averaging 
$40  per  ton,  which  would  give  a  total  product  for  the  camp  of  about 
$24,000;  the  total  production  is  probably  $30,000. 

The  veins  in  this  vicinity  differ  markedly  in  direction  and  dip  from 
those  at  other  camps  on  the  range.  Instead  of  a  strike  ranging  from 
east-west  to  northeast-southwest,  we  here  find  veins  striking  north- 
south  or  northwest-southeast,  and  with  a  dip  of  45°  to  50°  to  the  west. 
Though  base  ores  prevail,  some  of  the  veins  carry  a  notable  percent- 
age of  free  gold. 

The  more  prominent  claims  begin  at  the  Viola  mine  and  extend  for 
2^  miles  northward.  South  of  the  Viola  are  a  number  of  prospects, 
some  of  which,  such  as  the  Fraud  and  the  Ruby,  are  reputed  to  be 
promising. 

The  Black  Hornet  vein  extends  through  the  Viola  and  Ironsides 
claims,  but  can  hardly  be  traced  any  farther.  Having  at  first  a  direc- 
tion of  N".  20°  W.,  it  changes  in  the  Ironsides  claim  to  N.  40°  W.,  the 
dip  being  to  the  southwest  at  50°.  The  vein  crops  along  a  ridge  lead- 
ing up  to  Lucky  Peak,  and  a  sharply  cut  ravine  several  hundred  feet 
deep  offered  excellent  place  for  tunnels  to  tap  the  vein.  The  Viola 
shows  on  the  crumbling  granite  on  the  surface  as  a  strong  vein  of 
white  quartz.  It  is  developed  by  a  crosscut  tunnel  200  feet  long 


LIXDOKKN.]        DEPOSITS    OF    BLACK    HORNET    MINING    DISTRICT.  705 

and  a  drift  following  the  hanging  wall  north.  A  width  of  several 
feet  of  quartz  is  shown,  and  near  the  northern  end  of  the  claim  a  pay 
shoot  exists  100  feet  long  and  said  to  be  9  feet  wide,  carrying  an  ore 
which  averages  $15,  of  which  about  half  is  in  free  gold.  The  ore  is 
is  similar  to  that  of  the  Ironsides.  The  Ironsides  or  Black  Hornet 
adjoins  on  the  north,  and  its  principal  pay  shoot  lies  near  the  line  of 
the  Viola  claim.  It  is  developed  by  a  cross  cut  striking  the  vein 
about  100  feet  below  the  croppings  and  a  winze  sunk  100  feet  deep 
ear  the  southern  end-line  in  the  drift.  The  pay  shoot  extends  200 
feet  north  from  the  end  line,  but  only  70  feet  of  it  consists  of  shipping 
ore.  Along  the  pay  shoot  the  quartz  reaches  a  width  of  10  feet  or  more. 
This  block  of  ore  between  tunnel  level  and  surface  was  stoped  and 
shipped,  averaging,  it  is  said,  $40  per  ton,  almost  entirely  in  gold. 

North  of  the  richest  pay  shoots  are  large  amounts  of  lower-grade 
ore.  The  vein  shows  as  a  body  of  massive,  fine-grained  white  quartz, 
from  2  to  10  feet  wide,  and  contains  sulphides  irregularly  distributed 
through  it.  The  sulphides,  which  in  the  pay  shoot  will  amount  to  8 
per  cent  of  the  ore,  consist  of  arsenopyrite,  pyrite,  and  zinc  blende. 
The  value  is  by  no  means  exclusively  in  the  sulphides,  for  a  specimen 
of  massive  zinc  blende  and  arsenopyrite  assayed  only  0.40  ounce  of 
gold  and  4.60  ounces  of  silver;  a  total  value  of  $11.50.  A  sample  of 
the  quartz  with  scattered  iron  pyrite  yielded  0.45  ounce  of  gold  and 
1  ounce  of  silver;  a  total  value  of  $10.  The  walls  are  often  ill  defined 
and  without  a  clay  selvage,  and  consist  of  shattered  granite  and 
granite-porphyry  altered  by  thermal  processes.  The  feldspar  is 
largely  converted  to  sericite  or  white  mica,  and  the  rock  contains,  for 
a  few  feet  on  each  side  of  the  vein,  much  scattered  arsenopyrite. 
This  altered  wall  rock  contains,  in  strong  contrast  to  the  filling,  only 
a  trace  of  gold  and  silver.  The  Ophir  vein  lies  one-half  mile  north 
of  Ironsides  and  has  a  similar  direction.  But  little  work  has  been 
done  on  it.  Near  the  Ophir  vein  a  long  vein  begins,  and  extends, 
with  a  westerly  dip,  due  north  across  Dead  Dog  Creek  to  Deer  Creek. 
The  following  claims  are  located  on  it,  beginning  at  the  southern 
end:  Mclntyre,  Gray  Eagle,  Sorrel  Horse,  Golden  Rule,  and  Montana. 
Most  of  them  are  but  superficially  developed,  and  the  ore,  though 
free  milling  on  the  surface,  grows  base  at  a  slight  depth.  The  Mon- 
tana is  opened  by  a  cross  cut  270  feet  long. 

BOISE  MINING  DISTRICT. 

At  a  distance  of  from  3  to  5  miles  east  and  east-northeast  from 
Boise  are  a  number  of  prospects  which  have  never  produced  much, 
yet  are  worthy  of  mention.  The  country  rock  is  normal  granite 
throughout,  cut  by  a  few  dikes  of  granite-porphyry  with  a  general 
north-northwesterly  direction.  Dikes  of  dark  lamprophyric  rocks 
also  occur. 

18  GEOL,  PT  3 45 


706  IDAHO    MINING    DISTRICTS. 

Three  miles  east  of  Boise,  on  the  north  side  of  the  stage  road  in 
Cottonwood  Creek,  are  several  claims,  Morning  Star,  Last  Chance, 
and  First  Chance,  located  on  a  narrow  vein  striking  northeast-south- 
west and  dipping  south,  the  developments  consisting  only  of  two  tun- 
nels 100  feet  long.  High  assay  values  in  silver  have  been  found  on 
the  first  claim,  while  the  others  chiefly  contain  gold.  One  and  a  half 
miles  further  east,  just  north  of  the  road,  is  another  claim  said  to 
have  yielded  some  rich  decomposed  silver  ore. 

On  Picketpin  Gulch,  5  miles  east  of  Boise,  are  the  Golden  Star  loca- 
tion and  a  great  number  of  other  claims.  The  Golden  Star  claim  is 
said  to  cover  two  parallel  veins  and  a  cross  vein,  but  the  openings  do 
not  show  the  character  of  the  deposit  very  clearly  in  the  decomposed 
granite. 

An  arrastre  wa§  built  on  this  claim  many  years  ago  and  the  soft 
decomposed  ore  treated  in  it  is  said  to  have  yielded  $33  per  ton.  A 
small  mill  was  erected  a  few  years  ago,  but  it  did  not  run  long.  Man}7 
of  the  veins  in  this  vicinity  show  no  quartz,  but  only  a  streak  of  ther- 
mal alteration  on  each  side  of  a  fault  plane.  Mr.  Eldridge1  mentions 
at  this  same  locality  "several  narrow  dikes  of  lamprophyre,  trending 
N.  50°  to  70°  W.  and  dipping  45°  to  80°  SW.  A  vein  of  quartz  lies 
between  two  of  these."  The  dark-green,  fine-grained  dike  rock  from 
this  locality  is  panidiomorphic  granular,  and  consists  chiefly  of  brown 
hornblende  and  orthoclase  with  some  soda-lime  feldspar.  It  appears 
to  be  a  syenitic  lamprophyre  connected  with  the  vogesites.  In  the 
lower  part  of  Fivemile  Creek  many  strong  quartz  veins  appear,  all  of 
them  having  an  east-west  direction  and  a  southerly  dip  of  from  50° 
to  60°.  The  Scorpion  is  a  well-defined  vein  showing  2  to  3  feet  of 
solid  quartz  between  granite  walls.  A  tunnel  100  feet  long  has  been 
driven  in  this  vein  in  the  western  side  of  the  creek.  The  quartz, 
which  contains  scattered  iron  pyrite  and  arsenopyrite,  is  said  to  assay 
up  to  $8  per  ton.  A  dike  of  fine-grained,  dark-green  minette,  a 
species  of  syenitic  lamprophyre,  was  cut  in  the  lower  tunnel  and 
appears  to  lie  nearly  parallel  to  the  vein.  The  dike  is  considerably 
altered,  filled  with  calcite,  sericite  (white  mica),  and  pyrite,  and  car- 
ries about  $1.65  in  gold.  Claims  adjoining  on  the  same  vein  are  the 
Elevator  and  Hattie,  while  parallel  to  it  and  adjoining  •  northward 
are  the  Badger  and  Free  Gold.  Parallel  veins  also  lie  on  both  sides 
of  the  Idaho  City  stage  road  at  the  mouth  of  Fivemile  Creek,  and 
scattered  prospects  extend  eastward  to  Shaw  Mountain  district.  The 
Tornado  and  Blizzard  claims  are  situated  1  mile  northeast  of  the  Scor- 
pion, and  carry  heavy  sulphide  ore,  zinc  blende,  galena,  and  pyrite, 
having  high  assay  value  but  containing  no  free  gold. 

1  Sixteenth  Ann.  Bept,  U.  S.  Geol.  Survey,  Part  II,  1895,  p.  335. 


LINDGREN.]  SHAW    MOUNTAIN    MINES.  707 


SHAW  MOUNTAIN  MINING  DISTRICT. 

The  veins  in  this  district,  apparently  forming  a  continuation  of 
those  on  Fivemile  Creek,  were  discovered  in  1877.  The  veins  are 
located  on  the  high  ridge  just  north  of  the  Idaho  City  stage  road,  8 
miles  N.  80°  E.  from  Boise,  at  elevations  of  about  5,000  feet.  The 
mines  were  prospected  only  on  a  small  scale  in  1896.  The  country 
rock  is  normal  granite,  with  a  few  smaller  masses  of  granite-porphyry. 
A  strong  sheeting  of  the  granite  is  noted  in  many  places  between 
Fivemile  Creek  and  Shaw  Mountain,  the  joints  having  the  same 
strike  and  dip  as  the  veins.  The  Rising  Sun  vein  is  the  most  promi- 
nent, and  crops  as  a  well-defined  fissure  vein  of  white  quartz  for  1  mile 
near  the  summit  of  the  ridge  with  a  general  east-west  direction  and 
dip  of  45°  to  80°  S.  Four  claims  are  located  on  it,  from  west  to  east, 
as  follows:  Rising  Sun,  Paymaster,  North  Star,  and  Daisy.  On  the 
first  of  these  a  10-stamp  mill  was  erected  in  1879.  It  is  developed  by 
several  tunnels,  the  lowest  400  feet  below  the  croppings  and  500  feet 
long.  From  the  upper  levels  at  least  500  tons  were  extracted,  yield- 
ing from  $14  to  $100  per  ton;  in  the  lowest  tunnel  heavy  sulphide  ore 
was  found  which  did  not  contain  much  free  gold.  From  a  sample  of 
this,  collected  from  the  dump  and  containing  pyrite,  arsenopyrite, 
blende,  and  galena,  an  assay  of  11  ounces  of  gold  and  4  ounces  of 
silver  was  obtained,  a  total  value  of  $230  per  ton.  The  pay  shoot  is 
stated  to  be  120  feet  long,  the  width  of  the  vein  being  not  over  2  feet. 
Some  ore  of  similar  character  has  also  been  extracted  from  the  Pay- 
master. The  North  Star,  showing  strong  croppiugs  of  white  quartz 
on  the  summit  of  the  sharp  ridge,  is  said  to  contain  five  smaller  shoots 
of  ore,  and  is  opened  by  a  tunnel  280  feet  long,  giving  backs  of  180 
feet.  A  few  hundred  feet  south  of  this  vein,  on  two  smaller  parallel 
veins,  lie  several  claims,  among  which  are  the  Kessler,  Gold  King, 
and  Levi.  These  veins,  on  which  some  good  ore  is  said  to  have  been 
found,  carry  the  same  clean  white  quartz  as  the  North  Star;  samples 
of  this  barren-looking  material  gave  $2  in  gold  and  $0.49  in  silver. 

Near  the  vein  the  granite  has  undergone  the  usual  alteration  due  to 
thermal  waters.  The  brown  mica  (biotite)  is  converted  to  white  mica 
(muscovite),  and!  the  feldspars  are  changed  to  a  white  opaque  mass, 
which  is  muscovite  (sericite)  in  an  extremely  fine-grained  aggregate. 
Aggregates  of  coarse  muscovite  sometimes  occur  in  the  quartz  from 
this  vicinity. 

MINING    DISTRICTS    OF    WILLOW    CREEK    AND    ROCK    CREEK. 
LOCATION   AND   TOPOGRAPHY. 

The  Willow  Creek  district  lies  in  Boise  County,  18  miles  distant 
from  Boise,  in  a  direction  N.  20°  W.,  and  is  adjoined  on  the  northeast 
by  the  Rock  Creek  district,  the  two  extending  in  an  east-northeast 


708  IDAHO    MINING    DISTRICTS. 

direction  for  8  miles.  The  elevation  ranges  from  3,000  to  5,000  feet 
above  sea  level.  A  ridge  with  northwesterly  direction  and  culminat- 
ing in  Crown  Point  (elevation  5,300  feet)  separates  the  two  districts 
and  also  the  watershed  of  the  Boise  from  that  of  the  Payette.  Most 
of  the  mines  of  Willow  Creek  are  located  in  the  steep  gulches  at  the 
head  of  the  North  Fork  of  the  same  creek.  On  the  eastern  side  a 
steep  descent  leads  down  to  Rock  Creek,  draining  due  northward  into 
the  Payette.  The  eastern  end  of  Rock  Creek  district  lies  on  the  north- 
easterly trending  ridge  separating  the  Payette  from  the  branches  of 
Shafer  Creek.  The  mining  towns  of  Pearl  and  De  Levan  are  located 
on  Willow  Creek.  During  the  past  summer  there  were  probably  150 
men  in  the  districts.  A  small  Huntington  mill  is  erected  on  the 
Easter  claim,  and  two  smaller  custom  mills  are  also  built  lower  down 
on  Willow  Creek. 

While  placer  deposits  were  worked  in  the  vicinity  of  Willow  Creek 
long  ago,  and  one  of  the  mines  of  the  district,  the  Red  Warrior,  was 
worked  in  1870,  the  majority  of  the  locations  have  been  made  during 
the  past  few  years,  especially  in  1894  and  1895.  The  productive 
mines  of  the  districts  are  at  present  those  in  Willow  Creek,  and  the 
total  output  is  probably  about  $80,000  in  gold,  all  extracted  within 
the  last  few  years.  The  output  of  1896  is  estimated  at  $50,000. 
Among  the  producers  are  the  De  Levan  group,  the  Checkmate, 
Friday,  Leviathan,  Birthday,  and  Lincoln. 

GEOLOGY. 

GRANITIC   ROCKS. 

The  formation  of  chief  importance  as  containing  all  the  veins  is 
the  granite  and  associated  dike  rocks.  A  few  miles  west  of  Pearl  the 
first  granite  hills  emerge  from  under  the  cover  of  the  Payette  sand- 
stones and  rise  rapidly  eastward,  extending  thence  uninterruptedly 
in  a  northeasterly  direction.  The  larger  part  of  the  area  is  occupied 
by  a  granitic  rock,  which  is  a  local  modification  of  the  normal  granite 
of  the  Boise  Mountains. 

The  rock  crumbles  and  disintegrates  very  easily,  and  the  slopes  of 
the  mountains  are  covered  by  a  deep  mantle  of  disintegrated  rock. 
During  the  winter  rains  the  erosion  goes  on  very  rapidly,  and  deep 
gulches  are  often  excavated  in  a  remarkably  short  time.  It  is  possi- 
ble to  obtain  the  fresh  rock  only  from  exposures  in  the  bottom  of  the 
canyons  or  in  prospect  tunnels.  The  rock  is  of  a  light-gray  color  and 
has  a  coarse-grained  structure,  the  average  grain  having  a  diameter 
of  from  3  to  6mm.  It  is  composed  of  white  feldspar,  quartz,  biotite, 
and  sometimes  hornblende.  Brown  titanite  in  small  grains  is  uni- 
versally present.  Occasionally  larger  grains  of  light-red  orthoclase 
appear  among  the  prevailing  white  plagioclase.  Under  the  micro- 
scope the  following  minerals  are  noted :  Hornblende  appears  in  brown- 


u 

e 

n 

Z                                       r^ 

.2 

UJ 

z 

o 

z 

O 

a 

8 

z 

c 

UJ 

o 

UJ 
1 

LEISTO 

a. 

c 

3 
I 

ver  terr 

NEOCE 

O. 
Z 

,c 

LINDGEEN.] 


ROCK    OF    SILVER    WREATH    MINE. 


709 


ish-green  anhedral  grains,  and  biotite  as  irregular,  yellov/ish-brown 
foils.  The  quartz  occurs  in  abundant  anhedral  grains,  frequently 
exhibiting  undulous  extinction,  due  to  pressure.  The  feldspar,  also 
in  irregular  grains,  is  quite  predominantly  a  soda-lime  feldspar,  gen- 
erally an  oligoclase  or  andesine,  though  some  labradorite  was  found 
in  a  specimen  from  the  Payette  River  Canyon.  Small  plagioclase 
crystals  are '  sometimes  embedded  in  the  biotite.  Orthoclase  and 
microcline  both  occur  in  the  specimens  from  the  Silver  Wreath  mine 
and  near  the  Checkmate,  but  are  practically  absent  in  other  speci- 
mens from  the  Payette  River  Canyon,  3£  miles  east  of  Marsh.  A  lit- 
tle magnetite  and  apatite  always  occurs.  Titanite  is  present  in  larger 
quantities,  and  sometimes,  as  at  the  Silver  Wreath  mine,  makes  up  a 
notable  percentage  of  the  rock.  In  this  rock  it  occurs  in  idiomorphic 
wedge-shaped  crystals  protruding  in  feldspar  grains  and  also  includ- 
ing small  prisms  of  the  same  mineral.  An  analysis  of  the  rock  from 
the  Silver  Wreath  mirie  is  given  below,  and  a  calculation  of  the 
analysis  may  be  found  on  page  641 : 

Analysis  of  rock  from  the  Silver  Wreath  mine. 
[Analyst,  George  Steiger.] 


SiO3           .             ---  

65.23 

TiO2                                              

.66 

ALO, 

16.94 

Fe2O                                                          

1.60 

FeO            

1.91 

MnO                       .           .             --  -  

trace 

CaO                              -   -  -  

3.85 

BaO    -  

.19 

MffO 

1.31 

K2O                              -   -  

3.02 

Na,O                      -  -  

3.57 

H2O  below  100"                             

.18 

H2O  above  100°  -  ---  

.88 

p,O                                           

.19 

CO2                               

.25 

99.78 

According  to  these  data,  it  is  clear  that  the  granitic  rock  is  more 
closely  related  to  a  quartz-inica-diorite  than  to  a  granite,  and  shows 
great  similarity  to  the  granodiorite  of  the  Sierra  Nevada  in  California. 
Being,  however,  only  a  local  modification  of  a  large  area  of  normal 
granite,  with  which  it  is  connected  by  transitions,  the  name  granite 
has  provisionally  been  retained.  More  basic  dioritic  rocks,  contain- 
ing an  abundance  of  hornblende,  sometimes  appear  as  irregular 
streaks  and  masses  near  Pearl.  This  is  well  shown  in  the  tunnel  at 


710  IDAHO    MINING   DISTRICTS. 

the  Easter  mine,  as  well  as  in  the  bottom  of  the  creek  near  the  Silver 
Spray  claim. 

A  still  more  basic  facies  occurs  at  Horseshoe  Bend  on  both  sides  of 
the  river,  and  extends  for  a  distance  of  3  miles  down  along  the  can- 
yon, bordering  on  the  south  against  the  porphyritic  dike  subsequently 
described  and  on  the  north  against  the  dioritic  granite,  with  very  indis- 
tinct and  ill-defined  outline.  This  rock  varies  much  in  appearance, 
from  dark-gray,  medium-grained,  or  slightly  porphyritic  to  coarse- 
granular,  the  latter  consisting  apparently  of  white  feldspar  and  rather 
abundant  green. hornblende.  The  peculiarity  of  these  dark,  granular 
rocks  is  that  besides  being  poor  in  quartz  they  also  carry  augite,  and 
may  be  designated  pyroxene-diorites.  The  rock  at  the  Horseshoe 
Bend  bridge  carries  imperfectly  idiomorphic  augite  and  a  little 
hypersthene,  the  crystals  being  of  a  maximum  length  of  lmm,  but 
usually  less.  There  is  also  a  little  biotite.  These  three  constituents 
are  embedded  in  a  clear  feldspar  mass,  which  consists  of  short  prisms 
of  labradorite,  with  zonal  extinction,  cemented  by  smaller  anhedral 
grains  of  probably  the  same  feldspar.  The  structure  in  this,  as  in 
other  specimens,  is  hypidiomorphic  granular.  The  coarse-granular 
rock  three-fourths  mile  west  of  Horseshoe  Bend  consists  of  white 
feldspar,  green  hornblende,  and  a  smaller  amount  of  biotite  in  large 
sheets.  The  microscope  shows  a  few  large,  irregular  grains  of  ortho- 
clase,  in  which  are  embedded  smaller  prisms  of  labradorite.  In  this 
specimen  there  is  a  little  quartz  between  the  large  feldspars.  Most 
of  the  feldspar  grains  doubtless  consist  of  labradorite.  The  augite 
is  largely  converted  into  hornblende,  and  but  little  of  the  original 
mineral  remains. 

DIKE   ROCKS. 

A  series  of  dikes  extends  diagonally  across  the  districts.  Begin- 
ning as  narrow  dikes  near  the  Horseshoe  Bend  post-office,  these  rocks 
extend  in  a  widening  belt  over  toward  Rock  Creek,  there  attaining 
their  maximum  development  at  the  crossing  of  Rock  Creek.  The 
belt  is  here  fully  one-fourth  mile  wide,  and  practically  forms  one 
dike,  though  with  smaller  included  masses  of  diorite.  From  Rock 
Creek  this  same  dike  extends  up  toward  Crown  Point  Hill,  but  gradu- 
ally contracts  and  ends  before  reaching  the  summit.  Scattering  dikes 
are,  however,  found  on  that  hill,  and  appear  to  continue  from  there 
in  a  southwesterly  direction,  the  last  prominent  dike  appearing  near 
the  Dynamite  claim  at  Pearl. 

The  dike  rocks  are  of  somewhat  varying  character.  Pegmatitic  dikes 
hardly  occur  at  all,  and  light-colored  granite-porphyry,  so  common 
elsewhere,  is  not  abundant  here.  The  usual  dike  rock  is  a  coarse 
diorite-porphyrite.  The  rock  occurring  on  the  river  hill  between 
Horseshoe  Bend  and  Rock  Creek  is  prominently  porphyritic  by  large 
white  feldspar  crystals,  up  to  lcm  long,  and  by  smaller  crystals  of 


DIKE    ROCKS   ON   ROCK    CREEK.  711 

hornblende  and  biotite,  all  embedded  in  a  reddish  ground  mass. 
Under  the  microscope  the  feldspars  are  shown  to  be  a  plagioclase  of 
medium  basicity.  The  hornblende  and  the  biotite  are  of  normal  char- 
acter, while  the  groundmass  is  microcrystalline,  consisting  of  quartz 
and  unstriated  feldspar.  The  structure  of  the  groundmass  often  is 
approximately  micropoikilitic.  In  certain  of  these  porphyrites  horn- 
blende is  very  abundant  and  occurs  also  as  small  prisms  embedded 
in  the  groundmass. 

Another  kind  of  porphyry  contains  quartz  as  rounded  phenocrysts, 
and  in  this  variety  no  quartz  occurs  in  the  groundmass.  At  the  cross- 
ing of  Rock  Creek  the  dike  is  wide  and  fresh  and  the  rock  is  of 
somewhat  different  character.  It  is  dark  green  and  fine  grained,  with 
feldspar  prisms  up  to  8mm  in  length  and  a  few  black,  shining  crystals 
of  hornblende.  The  feldspar  is  chiefly  labradorite  in  sharp,  short 
.  prisms  and  very  fresh.  The  crystals  are  of  all  sizes,  grading  down 
to  those  which  form  a  part  of  the  groundmass.  Augite  occurs  as 
idiomorphic  crystals,  many  of  them  decomposed;  a  little  hornbler.de 
is  also  present,  and  magnetite  is  quite  abundant.  Between  the  closely 
crowded  feldspars  lies  very  little  groundmass  of  quartz  and  unstriated 
feldspar.  The  structure  of  this  rock  is  intermediate  between  holo- 
crystalliiie  porphyritic  and  panidiomorphic  granular.  The  rock  is 
thus  an  augite-diorite-porphyrite,  closely  connected  with  the  lampro- 
phyric  dike  rocks. 

At  the  Dynamite  claim,  near  Pearl,  dense,  dark-green  dikes  appear, 
consisting  of  clouded  and  altered  feldspar  in  lath-like  form,  between 
which  lie  the  decomposed  ferromagnesian  silicates  replaced  by  chlo- 
rite and  epidote.  This  rock  has  somewhat  the  appearance  of  an 
altered,  fine-grained  diabase.  Scattered  dikes  occur  in  other  parts  of 
the  district,  one  large  dike  cropping  on  the  road  to  Marsh,  1£  miles 
north  of  Pearl.  On  the  whole,  the  dikes  may  be  said  to  be  most 
abundant  for  a  distance  of  half  a  mile  north  and  half  a  mile  south  of 
the  main  belt  of  porphyritic  rocks  above  described. 

THE   PAYETTE  FORMATION. 

The  loose  sandstones  of  the  Payette  formation  (early  Neocene)  are 
laid  down  upon  the  very  irregular  granitic  surface  and  begin  at  the 
western  edge  of  the  Willow  Creek  district,  extending  far  westward. 
Sandstones  and  fine  gravels  of  the  same  age  are  also  found  high  up  in 
the  vicinity  of  Prospect  Peak,  and  cover,  in  fact,  the  pass  leading  from 
Willow  Creek  to  Boise.  A  branch  of  the  Payette  sandstones  extends 
in  a  northeasterly  direction  as  far  as  Horseshoe  Bend.  The  Payette 
formation  locally  contains  gold  placer  deposits,  as  at  Church's  ranch, 
at  the  southern  edge  of  Marsh  Valley.  The  gold  in  these  placers  has 
doubtless  been  washed  down  from  quartz  veins  on  the  northern  slope 
of  Crown  Point  Hill.  Other  placer  deposits  occur  1  mile  southwest 
of  Marsh  in  the  sands  and  conglomerates  of  the  Payette  formation. 


712  IDAHO    MINING    DISTRICTS. 

These  placers  also  probably  have  their  origin  in  the  gold  veins  of 
Crown  Point  Hill. 

RHYOLITE. 

The  sharp  point  of  Prospect  Peak  and  the  hill  1  mile  to  the  west  of 
it  consist  of  rhyolite.  They  are  necks  from  which  large  flows  of  the 
same  rock  poured  down  the  southern  slope  of  the  ridge  during  the 
period  of  the  Payette  lake  beds.  In  South  Willow  Creek  the  sand- 
stone is  seen  to  overlie  the  rhyolite.  A  smaller  flow  of  rhyolite 
reached  down  as  far  as  one-fourth  mile  south  of  Pearl.  The  rock  is 
usually  reddish  or  reddish-gray,  and  is  of  the  ordinary  compact  lith- 
oidal  variety.  In  the  last-mentioned  flow  occur,  associated  with  it, 
rhyolite  glass  and  loose  tuffs. 

BASALT. 

The  eruption  of  rhyolite  was  followed,  during  the  same  early  Neo-> 
cene  period,  by  extensive  eruptions  of  andesitic  basalt.  Smaller 
masses  and  necks  of  this  black  massive  rock  occur  on  the  ridge  one- 
fourth  mile  west  of  Prospect  Peak,  near  the  Leviathan,  and  at  several 
other  places  to  the  west. 

The  Payette  formation  and  accompanying  eruptives  are  later  than 
the  mineral  deposits,  and  contain  no  veins. 

THE    ORE   DEPOSITS. 

GENERAL  CHARACTER. 

The  gold  deposits  in  the  Willow  Creek  and  Rock  Creek  districts  are 
fissure  veins  of  somewhat  varying  character.  Most  of  them  occur  in 
a  belt  parallel  to  that  of  the  porphyry  dikes,  extending  in  a  north- 
easterly direction,  and  being  in  no  place  much  over  1  mile  in  width. 
The  veins  at  Willow  Creek  are  most  frequently  entirely  in  the  dioritic 
granite.  Sometimes  a  vein  follows  a  porphyry  dike  for  some  distance 
in  foot  or  hanging,  but  rarely  for  a  long  distance.  Again,  a  vein 
may  cut  through  a  dike,  in  which  case  it  often  splinters  up.  The 
porphyry  dikes  are  evidently  all  older  than  the  veins.  The  fis- 
sures which  carry  gold  strike  east- west  or  northeast-southwest.  In 
the  Willow  Creek  district  the  dip  is  always  to  the  north  from  45°  to 
80°  and  the  direction  east- west,  but  toward  Rock  Creek  the  direction 
gradually  changes  to  northeast-southwest.  Toward  Horseshoe  Bend 
the  direction  changes  again  to  east-northeast  to  west-southwest,  and 
the  dip  is  frequently  steep  to  the  south.  The  individual  veins  can 
rarely  be  traced  for  a  long  distance,  and  though  it  is  probable  that 
some  of  the  veins  are  a  mile  long,  this  can  rarely  be  satisfactorily 
proved.  Narrow  veins  predominate  in  the  Willow  Creek  district, 
while  wider  deposits  occur  on  Rock  Creek.  The  best  exposures  are, 
however,  found  in  the  former  district,  owing  to  more  extensive  devel- 
opment. In  Rock  Creek  the  developments  are  relatively  slight,  and 


LINDOHEN.]        GOLD    DEPOSITS    OF    WILLOW    AND. ROCK    CREEKS.        713 

the  decomposed  surface  material  does  not  always  allow  satisfactory 
conclusions  as  to  the  character  of  a  deposit.  A  large  number  of  loca- 
tions have  been  made  in  both  districts,  which,  in  fact,  contain  a  very 
great  number  of  veins.  The  ordinary  type  of  the  "Willow  Creek 
deposits  consists  of  one  or  more  fault  fissures,  on  both  sides  of  which 
there  is  a  zone  a  few  feet  wide  in  which  the  country  rock  has  been 
thoroughly  altered  (see  Chapter  II)  and  impregnated  with  pyrite. 
Along  the  main  fissure,  or,  if  there  are  two  or  more,  chiefly  along  the 
foot  wall,  there  are  narrow  seams  filled  with  sulphides  (pyrite,  zinc- 
blende,  arsenopyrite,  and  galena),  which  constitute  the  ore.  The 
altered  country  rock,  though  often  studded  with  pyrite  crystals,  usu- 
ally contains  only  $1  or  $2  in  gold,  while  the  value  of  the  solid  sul- 
phides in  the  seams  may  reach  $100  per  ton  or  more.  The  deposit 
may  thus  be  characterized  as  narrow  veins  of  high-grade  sulphide, 
ore.  There  is  usually  but  little  gangue  along  these  seams ;  calcite 
and  quartz  both  occur.  In  other  deposits  the  zone  of  altered  diorite 
or  granite  is  traversed  irregularly  by  numerous  small  seams  carrying 
arsenopyrite,  blende,  and  galena,  and  in  this  manner  the  wider  depos- 
its of  medium-grade  ore  are  formed.  The  veins  of  Rock  Creek  are 
generally  wider  than  those  of  Willow  Creek. 

The  surface  decomposition  attains  50  to  100  feet  in  depth.  In  this 
zone  the  vein  matter  forms  a  brown  ferruginous  mass,  which  contains 
free  gold  and  partly  decomposed  sulphides,  often  also  lead  carbonate. 
In  many  cases  the  fresh  sulphide  ore  is  found  less  than  50  feet  from 
the  surface.  The  fresh  ore  contains  a  very  small  percentage  of  free 
gold,  and  sometimes,  in  rich  ore,  not  even  a  color  is  obtained  by  the 
pan.  It  follows  from  this  that  the  amalgamation  process,  is,  as  a 
rule,  applicable  only  to  the  surface  ores,  though  some  veins  will  be 
found  to  contain  more  free  gold  than  others.  At  present  the  rich 
ore — all  above  $30 — is  sacked  and  shipped  to  smelters. 

The  minerals  consist  of  the  following  combination,  so  common  in 
the  Boise  Ridge:  pyrite,  arsenopyrite,  zinc  blende,  and  galena;  chal- 
copyrite  is  rare.  The  first  two  often  occur  as  crystals.  The  zinc 
blende  is  black,  brown,  or  greenish-yellow,  usually  not  crystallized. 
The  galena  is  less  common  than  the  others,  and  is  considered  an  indi- 
cation of  rich  ore.  Ruby  silver  is  reported  as  a  rarity  from  the 
Shamrock  and  the  Lincoln. 

Shipping  ore  often  contains  5  ounces  of  gold  and  5  ounces  of  silver 
to  the  ton.  A  sample  of  pyrite,  arsenopyrite,  and  galena  from  one 
of  the  best  mines  gave  0.85  ounce  of  gold  and  28.35  ounces  of  silver 
per  ton,  a  total  of  $37.42.  Some  galena  carries  60  to  70  ounces  of  sil- 
ver, and  generally  also  much  gold.  Much  of  the  arsenopyrite  and 
zincblende  is  poor.  The  principal  value  appears  to  be  in  the  pyrite 
and  galena.  Of  the  extent  and  direction  of  the  ore  shoots  but  little 
is  known  at  present,  but  it  is  clear  that  the  high-grade  shoots  are  not 
of  great  lateral  extent  and  that  they  are  rather  irregular. 


714  IDAHO    MINING   DISTRICTS. 

TREATMENT  OF  THE  ORES. 

At  present  only  the  shipping  ores  can  be  utilized,  and  the  question 
how  to  make  $10  to  $20  ore  pay  is  one  of  the  greatest  importance  to 
the  camp.  If  it  should  contain  any  notable  amount  of  free  gold,  amal- 
gamation and  concentration  will  probably  be  found  most  economical. 
Experiments  should  be  made  as  to  the  applicability  of  the  cyanide 
process  to  these  ores.  In  the  absence  of  notable  amounts  of  copper 
and  antimony  the  process  might  be  of  advantage,  but  experiments 
are  necessary  to  prove  this. 

DETAILED   DESCRIPTION. 

The  Lincoln  vein  is  one  of  the  most  westerly  locations  in  Willow 
Creek,  being  situated  about  a  mile  south-southwest  of  Pearl.  The 
strike  is  N.  76°  W.  and  the  dip  steep  to  the  north,  the  vein  being 
traceable  in  granite  for  a  distance  of  one-fourth  mile,  with  good  ore 
at  close  intervals.  The  tunnel  shows  2  to  10  feet  of  altered  and 
pyritic  granite,  with  smaller  streaks  and  veins  (1  to  6  inches  wide)  of 
pyrite,  arsenopyrite,  and  blende,  associated  with  a  little  drusy  quartz; 
ruby  silver  has  been  noted.  The  developments  consist  of  a  crosscut 
tunnel  200  feet  long,  with  drifts  on  the  vein,  and  a  small  winze. 
Fifteen  tons  of  ore  were  shipped,  averaging  $100.  A  sample  of  poor 
ore  gave  0.1  ounce  of  gold  and  5.30  ounces  of  silver,  a  relatively  large 
amount  of  silver  for  this  camp. 

The  Shamrock  is  situated  a  few  hundred  feet  southwest  of  Pearl 
post-office,  and  is  developed  by  an  80-foot  crosscut  from  the  creek 
level,  from  which  drifts  extend  on  the  vein.  The  country  rock  is 
very  much  disturbed  granite  containing  rich  but  irregular  seams  of 
ore.  Some  tons  of  the  latter  were  shipped  to  smelters. 

The  Pinto  lies  a  short  distance  north  of  the  Bishopric  mill,  in 
Pearl,  and  has  been  opened  by  225  feet  of  tunnels  and  a  50-foot  winze. 
Sixty  tons  of  ore  are  said  to  have  been  milled,  yielding  $23  per  ton. 
The  vein  is  about  2  feet  wide.  The  Pearl  claim,  showing  some  very 
good  ore,  is  located  in  this  vicinity. 

The  Dynamite,  said  to  be  the  extension  of  Pinto,  is  situated  on  the 
north  side  of  Willow  Creek,  a  short  distance  east  of  Pearl,  the  crop- 
pings  being  250  feet  above  the  stream.  The  vein  is  opened  by  a 
tunnel  200  feet  long,  strikes  N.  68°  W.  and  dips  45°  N.,  and  shows 
16  inches  of  decomposed  vein-matter  in  granite.  A  large  porphyry 
dike  lies  close  by  to  the  north. 

The  Easter  lies  very  nearly  in  the  continuation  of  the  Dynamite, 
and  is  one  of  the  producing  veins  of  the  district.  The  croppings  lie 
in  granite  250  feet  above  the  creek  and  the  vein  is  developed  by  a 
tunnel  100  feet  below  the  croppings.  Another  tunnel  was  started  at 
the  creek  level,  but  has  not  yet  reached  the  vein,  work  being  sus- 
pended in  1896  on  account  of  litigation.  A  considerable  amount  of 


LINDGBEN.]  MINES    ON    WILLOW    CREEK.  715 

ore  was  sloped  and  milled  in  1895.  The  vein  strikes  N.  81°  W.,  dips 
60°  N.,  and  shows  2  to  3  feet  of  decomposed  vein  matter  which,  in  the 
pay  shoot,  yielded,  it  is  said,  $38  per  ton  of  free  gold.  Pockets  carry- 
ing extremely  rich  ore  occurred  at  intervals.  On  the  west  side  the 
vein  is  said  to  splinter  up  in  a  porphyry  dike. 

The  Iron  Dollar  is  located  a  short  distance  east  of  the  Easter,  and 
is  probably  the  continuation  of  the  same  vein.  The  development 
consists  of  short  tunnels  and  surface  cuts.  A  few  tons  have  been 
milled,  yielding  $58  in  free  gold.  The  vein,  which  strikes  N.  71°  W. 
and  dips  60°  N.,  lies  in  granite  with  occasional  porphyry  dikes  in  the 
hanging  wall.  The  decomposed  ore  consists  of  altered  granite,  with 
streaks  of  arsenopyrite,  pyrite,  and  galena,  as  well  as  a  little  calcite 
and  quartz.  A  sample  of  good  ore  gave  2.50  ounces  of  gold  and  7.15 
ounces  of  silver  to  the  ton,  a  total  of  $56.68. 

The  Judas  lies  a  few  hundred  feet  north  of  the  Iron  Dollar,  and  is 
at  present  (1897)  being  developed  by  a  shaft  intended  to  reach  a 
depth  of  400  feet.  Excellent  ore  is  reported  to  have  been  milled  from 
this  vein.  The  strike  and  dip  are  nearly  the  same  as  in  the  Iron 
Dollar,  and  the  vein  shows  from  1  to  2  feet  of  decomposed  granite 
carrying  rich  seams. 

The  Checkmate  crops  in  granite  on  the  south  side  of  Willow  Creek, 
due  south  of  the  Judas.  This  vein  is  one  of  the  productive  proper- 
ties, shipping  ore  during  the  whole  summer  of  1896.  It  is  reported 
that  300  tons,  averaging  $80  per  ton,  have  been  shipped.  The  mine 
is  developed  by  a  tunnel  100  feet  long  on  the  level  of  the  creek,  giving 
about  100  feet  of  backs.  The  deposit  consists  of  a  zone  several  feet 
wide  of  altered  and  pyritic  granite,  containing  rich  seams  of  heavy 
sulphides,  arsenopyrite,  pyrite,  blende,  and  galena.  At  the  time  the 
mine  was  visited  most  of  the  ore  came  from  a  seam  of  solid  sulphides 
4  to  6  inches  wide.  The  strike  is  1ST.  84°  W. ;  the  dip  to  the  north. 

A  short  distance  east  of  the  Checkmate  is  the  Silver  Spray,  from 
which  some  good  ore  has  been  shipped.  The  vein  is  opened  by  a  short 
tunnel,  and  strikes  east-west,  dipping  40°  N.  The  country  rock  is 
dioritic  granite,  with  streaks  of  dark  diorite  and  dikes  of  diorite- 
porphyrite.  The  character  and  the  minerals  are  similar  to  the 
Checkmate. 

A  little  farther  east  is  the  Golden  Chest,  showing  a  wide  zone  of 
altered  and  pyritous  granite  with  narrow  seams  of  zinc  blende. 

South  of  Willow  Creek,  opposite  the  last-named  claim,  lies  the  Red 
Warrior,  the  oldest  location  in  the  district.  No  work  was  done  on  it 
in  1896. 

One  mile  southeast  of  Pearl,  on  the  summit  of  a  ridge,  lies  the 
Leviathan  claim.  This  is  developed  by  a  shaft  75  feet  deep,  and  a 
few  tons  of  rich  ore  have  been  shipped.  The  width  of  the  mineralized 
granite  is  13  feet,  with  seams  of  pay  ore  on  both  walls.  In  the  con- 
tinuation of  this  claim  lie  the  Middleman  and  the  Sacramento,  which 


716  IDAHO   MINING   DISTRICTS. 

have  the  same  east- west  strike.  Both  of  these  claims  have  shipped 
some  rich  ore,  containing  much  galena.  The  pure  galena,  assays  8 
ounces  of  gold  and  67  ounces  of  silver  to  the  ton.  The  developments 
are  slight. 

The  Friday  is  located  on  a  flat  100  feet  south  of  the  Leviathan  and 
is  developed  by  a  100-foot  shaft  and  drifts  on  the  vein.  Thirty  tons 
of  ore  are  said  to  have  been  shipped  and  some  rich  surface  ore  has 
been  milled.  The  deposit  shows  8  feet  of  altered  granite,  with  a  seam 
of  heavy  sulphides  on  the  foot  and  hanging -walls.  The  ore  contains 
pyrite,  arsenopyrite,  and  blende,  with  much  calcite.  This  vein  is  said 
to  be  nearly  vertical.  The  mine  was  not  accessible  during  the  present 
examination. 

Beyond  the  claims  mentioned,  for  a  distance  of  about  1,000  feet,  there 
are  but  few  locations,  but  a  number  of  strong  veins  are  found  on  the 
summit  of  the  ridge  separating  Willow  Creek  from  Rock  Creek. 

Beginning  on  the  north,  the  Emmett  vein  is  located  near  the  summit 
of  Crown  Point  Hill,  on  the  southwesterly  slope.  Good  ore  is  reported 
to  have  been  found  in  this  claim  and  shipments  were  made  during 
the  winter  of  1896-97.  An  incline  shaft  is  sunk  to  a  depth  of  100  feet. 

The  Ida  lies  on  the  Rock  Creek  slope,  at  an  elevation  of  4, 700  feet, 
and  appears  to  be  a  wide  vein  in  a  dike  of  mineralized  porphyry.  It 
is  developed  by  175  feet  of  tunnels  and  shaft,  and  excellent  assays 
have  been  obtained  from  average  samples.  The  Blaine,  on  the 
Willow  Creek  side,  a  short  distance  north  of  the  road  to  Rock  Creek, 
is  a  promising  prospect  from  which  some  ore  was  shipped  in  1896. 
The  Alexander,  located  on  the  divide,  showed  some  good  ore,  a  brown 
decomposed  mass  containing  lead  carbonate  and  milling  $40  per  ton. 
The  vein  is  4  feet  wide,  striking  N.  74°  E.  and  dipping  north. 

The  Birthday,  a  few  hundred  feet  south  of  the  Blaine,  has  produced 
some  rich  shipping  ore,  composed  of  solid  pyrite,  zinc  blende,  and 
galena. 

The  Silver  Wreath  lies  on  the  Willow  Creek  side,  three-fourths  of 
a  mile  southeast  of  Crown  Point  Hill,  and  is  opened  by  a  crosscut 
170  feet  long,  cutting  the  vein  at  a  depth  of  75  feet.  The  croppings 
show  distinctly  by  quartz,  colored  greenish  by  arsenic.  The  strike  is 
N.  79°  E.  and  the  dip  steep  to  the  north.  The  deposit  consists  of  a 
zone  of  decomposed  dioritic  granite,  8  feet  wide,  containing  seams  of 
the  usual  minerals.  Some  ore  shipped  yielded  $40  per  ton. 

The  IXL  is  situated  on  the  Rock  Creek  side,  three-fourths  of  a  mile 
east-southeast  of  Crown  Point  Hill.  An  incline  shaft  is  being  sunk 
on  this  vein,  and  has  at  the  present  writing  attained  a  depth  of  200 
feet.  The  vein,  which  strikes  on  an  average  northeast  and  dips 
50°  N. ,  is  contained  in  granite  with  a  dike  of  granite-porphyry  in  the 
hanging  wall.  Four  feet  of  brown  decomposed  vein  matter  are  shown 
in  the  shaft.  About  25  per  cent  of  the  total  value  is  in  free  gold,  and, 
according  to  average  samples,  there  is  a  considerable  body  of  medium- 


UKDQBKN.]  MINES    ON   WILLOW   AND    ROCK   CREEKS.  717 

grade  ore.  A  tunnel  is  located  on  the  eastern  extension,  900  feet  east 
of  the  incline.  It  is  claimed  that  several  ore  bodies  occur  between 
the  incline  and  the  shaft.  The  vein  is  one  of  the  longest  in  the  dis- 
trict, being  traceable  for  at  least  2,000  feet. 

The  Zena,  Stella,  and  Ella  claims  are  located  600  feet  south  of  the 
IXL,  about  in  the  continuation  of  the  Birthday  and  Silver  Wreath,  on 
the  Willow  Creek  side,  and  are  opened  by  several  short  tunnels.  The 
Zena  shows  a  well-defined  fissure  with  a  dike  of  diorite-porphyrite 
5  feet  wide  in  the  hanging.  The  ore  consists  of  narrow  streaks  of 
blende,  pyrite,  and  arsenopyrite  in  an  altered  and  pyritous  granite. 
The  ore  appears  fresh  near  the  surface,  in  contrast  to  the  decomposed 
ledge  matter  of  the  IXL  and  the  Alexander. 

A  number  of  veins  are  located  along  Rock  Creek.  The  Black  Crook 
lies  ITJ-  miles  northeast  of  Crown  Point  Hill,  and  is  opened  by  a  drift 
on  the  vein  140  feet  long.  The  vein  strikes  N.  62°  E.  and  has  a  maxi- 
mum width  of  8  feet.  It  has  diorite-porphyrite  in  the  hanging  wall 
and  granitic  graiiite-diorite  in  the  foot  wall.  The  gangue  is  a  grayish 
quartz  and  a  pink  calcite  colored  by  manganese.  The  ore  body  was 
reported  to  be  large  but  of  low  grade.  Some  assays  show  a  relatively 
large  amount  of  silver  in  the  ore.  The  Vein  is  reported  to  be  traceable 
for  a  long  distance  eastward. 

The  Blue  Bucket  lies  1,500  feet  farther  down  the  creek,  at  an  eleva- 
tion of  3,500  feet,  in  diorite  and  dioritic  granite.  Some  very  rich  ore 
is  said  to  have  been  taken  from  it,  but  the  claim  was  not  worked 
during  the  examination  of  the  district. 

East  of  Rock  Creek  lie  a  large  number  of  claims,  on  most  of  which 
but  little  work  had  been  done  in  1896.  Among  them  is  the  Anticlinal, 
under  the  Liberty  Cap  Hill,  and  the  Lambertine,  Bobtail,  and  Mint 
claims,  three-fourths  of  a  mile  east  of  Rock  Creek.  On  the  Bobtail 
claim  a  tunnel  200  feet  in  length  has  been  run,  cutting  an  8-foot  vein 
of  good  ore. 

Many  claims  are  also  located  on  the  ridge  between  Shafer  Creek 
and  the  Payette  River.  There  appear  to  be  two  principal  lines  of 
deposits.  One  begins  one-half  mile  southwest  of  Horseshoe  Bend 
post-office,  where  the  granite  emerges  from  the  Payette  lake  beds  and 
continues  in  a  west-southwest  direction  up  to  the  summit  of  the  ridge. 
Among  the  claims  located  along  this  line  are  the  Sunny  Side  and  the 
Ballentyne,  both  on  the  same  vein.  The  vein  dips  70°  to  80°  S.  and 
is  about  2  feet  wide.  The  vein  matter  is  soft  and  decomposed,  carry- 
ing free  gold  and  some  lead  carbonate.  The  country  rock  is  granite, 
but  in  the  foot  wall  lies  a  dike  of  quartz-diorite-porphyrite  a  few  feet 
wide.  Another  vein  lies  a  short  distance  southward.  A  large  num- 
ber of  prospects  are  found  on  the  steep  river  hill  toward  the  Payette, 
about  one-fourth  mile  north  of  the  Ballentyne  and  opposite  McFar- 
land's  ranch  on  the  river.  The  following  claims  are  located  on  this 
vein  system,  from  east  to  west:  Mammoth,  Apex,  Atlanta,  Claggett, 
Topeka,  Kentuck.  These  are  at  an  elevation  of  about  1,000  feet  above 


718  IDAHO    MINING   DISTRICTS. 

the  river.  Hall's  claim  lies  a  little  lower  down,  about  700  feet  above  the 
river.  Some  of  these  claims  appear  to  be  promising  properties,  but 
the  developments  are  slight.  The  ores  are  decomposed,  carrying  on 
the  surface  a  considerable  amount  of  free  gold.  Some  antimonite, 
carrying  no  gold,  was  also  found  in  this  vicinity. 

The  above  are  by  no  means  all  of  the  claims  and  prospects  of  the 
district,  but  only  such  as  showed  any  notable  development  or  pro- 
duction of  ore.  It  is  quite  possible  that  some  of  these  prospects  may 
develop  into  paying  mines. 

.  SILVER   DEPOSITS. 

The  Boise  Mountains  contain  many  notable  silver  deposits,  chiefly 
well-defined  quartz  veins  with  finely  distributed  rich  sulphides  and 
antimonides.  But  it  is  not  intended  to  take  up  the  study  of  them  in 
this  paper.  The  principal  locality  where  silver  mining  has  been  car- 
ried on  is  at  Banner,  25  miles  northeast  of  Idaho  City. 

Many  scattered  quartz  veins  with  silver  ores,  either  galena  or  rich, 
silver  sulphides,  occur  in  the  area  here  described,  but  none  of  them 
have  produced  much.  A  few  deposits  of  this  kind  occur  along  the 
Idaho  City  road  3  or  4  miles  from  Boise,  and  another' in  north  fork  of 
Dry  Creek  a  few  miles  southwest  of  Shafer  Butte.  Other  silver  pros- 
pects are  located  2  miles  south  of  Church's  placers,  in  Marsh  Valley, 
and  at  several  places  near  Horseshoe  Bend,  notably  on  the  western 
side  of  the  Payette  2  miles  north  of  the  bridge.  Many  silver  pros- 
pects occur  1  mile  east  of  Halfway  House  in  the  Moore  Creek  Valley, 
and  some  of  them  are  said  to  contain  rich  ore  (Sunlight  group). 

The  occurrence  of  occasional  silver  deposits  in  the  Idaho  Basin  has 
already  been  mentioned  in  the  detailed  description  in  Chapter  IV. 

PLACERS  OF  THE  BOISE  RIDGE. 
RECENT  PLACERS. 

The  bars  of  the  Boise  and  Payette  rivers  were  worked  in  the  early 
days,  and  on  some  of  them  work  is  still  progressing.  The  large 
gravels  of  the  lower  reaches  of  both  rivers  contain  a  little  gold,  but 
scarcely  enough  for  profitable  working.  A  dredger  built  some  years 
ago  to  work  the  gravels  of  the  lower  Payette  near  Marsh  proved  a 
failure.  The  placers  of  the  Moore  Creek  drainage  were  discussed  in 
Chapter  III.  Most  of  the  creeks  of  the  Boise  Range  have  carried  a 
little  gold,  but  few  of  them  have  been  rich. 

Benches  along  Dry  Creek  and  Willow  Creek  are  worked  at  inter- 
vals, even  now,  when  water  is  available.  Shafer  Creek,  at  least  the 
branch  heading  near  Cartwright  ranch,  carried  a  little  gold.  The 
richest  placers  probably  occur  at  the  northern  base  of  Crown  Point 
Hill  at  Church's  in  Marsh  Valley;  but  the  whole  output  of  the  recent 
placers  of  the  Boise  Ridge  is,  if  we  except  the  basin,  of  small 
importance. 


UNDGHBN.]  PLACERS    OF    THE    BOISE    RIDGE.  719 

NEOCENE  PLACERS. 

The  shore  and  old  gulch  gravels  resting  on  granite  in  the  early  Neo- 
cene Payette  formation  carry  a  little  gold  at  many  places — for  instance, 
in  several  gulches  about  2  miles  eastward  from  Boise,  north  and  south  of 
the  Idaho  City  stage  road.  Similar  old  placer  deposits  are  found  in 
the  Payette  formation  at  Church's,  in  Marsh  Valley,  and  the  old  grav- 
els at  Johnson's,  1  mile  southwest  of  Marsh,  contain  some  gold  which 
has  been  concentrated  in  the  gulches  and  washed  by  the  hydraulic 
process. 

Gold-bearing  gravels  of  late  Neocene  (Pliocene)  age  are  found  below 
the  remnants  of  the  several  basalt  flows  on  both  sides  of  Boise  River, 
those  in  Moore  Creek  having  already  been  mentioned.  The  top  of  the 
lowest  flow,  which  is  probably  the  oldest,  lies  at  the ' '  New  York  House," 
10  miles  southwest  of  Boise,  at  the  level  of  the  river,  and  is  not  visible 
farther  west.  Eastward  it  rises  slowly,  and  near  the  mouth  of  Moore 
Creek  is  40  feet  above  the  river  (in  August).  Below  this  flow,  which 
is  about  20  feet  thick,  lie  2  to  10  feet  of  coarse,  heavy  gravel,  resting 
on  granite.  This  gravel  is  in  places  rich  in  coarse  gold,  part  of  which 
probably  conies  from  seams  and  small  veins  in  the  surrounding  gran- 
ite. There  are  only  a  few  exposures  of  this  low  flow  below  the  mouth 
of  Moore  Creek,  and  it  is  reported  that  only  one  or  two  are  known 
above.  The  flow  came  down  the  south  fork  of  the  Boise.  At  low 
water  this  gravel  below  the  basalt  has  been  mined  with  profit  at  sev- 
eral places,  notably  at  the  Holy  Terror  mine,  2  miles  below  the  mouth 
of  Moore  Creek,  and  at  Tarents,  2  miles  farther  down.  There  is  only 
a  limited  amount  of  this  gravel  below  the  lower  flow.  The  two  other 
flows,  30  to  60  feet  thick,  are  at  elevations  of  120  and  300  feet  above 
the  river.  Underlying  both  of  them,  wherever  they  are  preserved, 
hanging  along  the  banks  of  the  canyon,  are  heavy  masses  of  late  Neo- 
cene gravels,  20  feet  or  more  in  thickness.  This  gravel  contains  some 
gold  throughout,  and  though  much  of  it  is  fine,  it  may  in  places  be 
found  rich  enough  for  the  hydraulic  process  wherever  water  can  be 
brought  to  it.  In  1896  an  attempt  was  made  at  the  mouth  of  the 
canyon,  8  miles  southeast  of  Boise,  on  the  northeast  bank  of  the  river, 
to  mine  the  heavy  mass  of  gravel  and  sand  here  underlying  the  basalt 
flow,  and  should  this  attempt  be  successful  there  are  probably  many 
other  similar  deposits  a  little  farther  up  the  river  which  could  be 
worked  in  the  same  manner. 


THE  FOSSIL  PLANTS  OF  THE  PAYETTE  FORMATION. 


By  F.  H.  KNOWLTON. 


The  following  report  is  based  on  a  collection  of  fossil  plants  obtained 
during  the  past  season  by  Mr.  Waldemar  Lindgren  from  the  lake  beds 
of  the  Snake  River,  in  western  Idaho,  to  which  the  name  Payette  for- 
mation has  been  given.  The  matrix  in  which  the  plants  are  preserved 
is  in  general  a  fine-grained  clay,  which  has  retained  their  outline  and 
nervation  with  remarkable  fidelity. 

Following  is  a  list  of  localities  from  which  the  plants  were  obtained : 

1.  Two  miles  southeast  of  Marsh  post-office,  Boise  County,  Idaho. 
From  a  coal  prospect. 

2.  One  mile  southeast  of  Marsh  post-office,  Boise  County,  Idaho. 
From  a  canyon  on  the  road  to  Willow  Creek  and  several  hundred 
feet  above  the  Payette  River. 

3.  Robb's  coal  prospect,  1  mile  south  of  Horseshoe  Bend  post-office, 
Boise  County,  Idaho. 

4.  Cartwright's  ranch,  on  Shafer  Creek,  4  miles  southeast  of  Horse- 
shoe Bend  post-office,  Boise  County,  Idaho. 

5.  Near  Idaho  City,  Boitee  County,  Idaho. 

SYSTEMATIC  ENUMERATION  OF   SPECIES. 

DRYOPTERIS  IDAHOENSIS  n.  sp. 
PL  XCIX,  figs.  1,  2. 

Outline  of  frond  unknown;  frond  twice  pinnate,  pinnse  approxi- 
mate, subopposite,  deeply  pinnate,  the  segments  oblong,  obtusely 
acuminate,  or  upper  pinnse  lobed  at  base,  the  remainder  entire  or 
undulate;  secondary  rachis  strong,  curved  upward;  each  segment 
with  a  strong  midvein  giving  off  forked  veins. 

As  may  be  seen  from  the  figure,  this  species  is  represented  only  by 
a  fragment,  which,  were  it  not  for  the  fact  that  it  is  so  distinctly 
unlike  any  previously  described  American  form,  would  be  almost  too 
fragmentary  for  notice.  The  original  form  of  the  frond  can  not  be 
determined.  The  specimen  consists  of  a  portion  of  the  rachis  with 
parts  of  four  pinnse,  only  two  of  which  are  approximately  perfect. 
The  pinnae  are  close  together,  subopposite  in  attachment,  and  slightly 
18  GEOL,  PT  3 46  ?21 


722  IDAHO   MINING   DISTRICTS. 

arching  upward.  The  lowest  pinna  is  lanceolate,  deeply  cut,  with 
oblong,  obtusely  acuminate  segments.  It  is  2cra  in  length.  The  other 
most  perfect  pinna  is  1.5cm  in  length,  and  is  also  lanceolate  in  outline, 
but  has  only  one  pair  of  segments  at  base,  the  remainder  being  merely 
undulate.  The  nervation  consists  of  forked  veins  arising  from  a 
rather  strong  midvein  in  each  segment. 

As  no  fruit  is  preserved,  its  proper  generic  reference  becomes  ques- 
tionable, and  dependence  must  be  placed  on  its  resemblance  to  the 
described  forms  of  which  the  systematic  position  is  known.  It  has, 
for  example,  some  resemblance  to  what  has  been  described  as  Las- 
trc&a  fischeri  Heer,  from  the  Swiss  Tertiary,  and  also  John  Day  Val- 
ley, Oregon,  but  differs  in  being  hardly  one-half  the  size  and  in 
having  forked  instead  of  simple  nerves. 

On  the  whole,  this  appears  to  approach  most  closely  certain  species 
of  Aspidium  (now  Dryopteris)  from  the  Tertiary  of  Switzerland. 
Among  them  may  be  mentioned  A.  filix-antiqua  Heer,  A.  meyeri 
Heer,  and  A.  elongatum  Heer,  all  described  and  figured  in  Heer's 
Flora  Tertiaria  Helvetia?,  Vol.  I,  PI.  XL 

Locality:  One  mile  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 

EQUISETUM  sp. 

There  are  several  Equisetum  stems  in  the  collection.  They  are  all 
underground  portions  of  stems,  showing  the  scars  of  rootlets.  From 
one  stein  that  is  shown  in  cross  section  it  appears  that  they  are  about 
12-ribbed.  They  vary  in  width  from  lcm  to  2cm. 

These  stems  appear  to  most  resemble  E.  ivyomingense  Lx.,1  from  the 
vicinity  of  Green  River,  Wyoming,  also  identified  by  Newberry2  at 
probably  the  same  locality,  but  there  are  differences,  which  make  it 
advisable  to  keep  them  apart.  I  have  not  given  a  name  to  this  form, 
hoping  that  more  and  better  material  could  be  obtained. 

Locality:  Idaho  City,  Idaho. 

PlNUS    Sp. 

PI.  XCIX,  fig.  3. 

The  collection  contains  a  single  nearly  perfect  fruit. 
Locality:  Idaho  City,  Idaho. 

SEQUOIA  ANGUSTIFOLIA  ?  Lx. 

PI.  XCIX,  fig.  4. 
Sequoia  angustifolia  Lx.,  Cret.  and  Tert.  Fl.,  p.  240,  PI.  L,  fig.  5,  1883. 

This  species  was  described  by  Lesquereux  from  Elko  Station, 
Nevada,  in  strata  supposed  to  be  of  Green  River  Group  age.  He  also 
reported  the  same  species  from  Corral  Hollow,  California.  The  figure 

»  Tert.  PL,  p.  69,  PL  VI,  figs.  8-11. 
a  Of.  plates  ined.,  PL  LXV,  flg.  8. 


KNOWLTON.]  PLANTS    OF    THE    PAYETTE    FORMATION.  723 

of  a  specimen  from  this  last  locality,  as  cited  above,  agrees  closely 
with  the  one  under  discussion,  but  it  does  not  appear  to  be  identical 
with  the  Elko  specimens.  It  is  likely  that  on  a  revision  of  American 
fossil  Sequoias  this  will  have  to  be  made  a  new  species,  unless  it  can 
be  correlated  with  some  known  form. 

Localities:  Two  miles  southeast  of  Marsh  post-office,  Boise  County; 
Cartwright's  ranch,  on  Shafer  Creek;  Idaho  City. 

SEQUOIA,  Cones  of. 

The  collection  contains  a  single  example,  which  bears  three  broken 
cones  that  appear  to  belong  to  this  genus.  They  are  too  fragmentary 
to  make  an  identification  of  value. 

Locality:  One  mile  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 

JUGLANS   HESPERIA  n.  sp. 

PI.  XCIX,  fig.  8. 

Leaflet  coriaceous,  elliptical-lanceolate  in  outline,  unequal-sided  at 
base,  probably  acuminate  at  apex  (broken);  margin  finely  serrate; 
petiole  short,  thick;  midrib  thick;  secondaries  numerous,  about 
eighteen  pairs,  opposite  below,  alternate  above,  emerging  at  a  low 
angle,  but  curving  upward,  and  running  along  the  border  and  send- 
ing weak  branches  to  the  teeth;  intermediate  secondaries  numerous, 
often  two  between  secondaries,  either  soon  lost,  or  running  nearly  to 
the  margin;  nervilles  numerous,  mainly  percurrent;  finer  nervation 
quadrangular. 

This  fine  species  is  represented  by  the  single  example  figured.  It 
is  nearly  perfect,  lacking  only  the  apex.  The  part  preserved  is  8om 
long  and  was  probably  10om  or  llcm  in  length  when  perfect.  It  is 
broadest  in  the  middle,  at  which  point  it  is  3.75cm  in  width.  It 
is  broadly  lanceolate,  rounded  and  unequal-sided  at  base,  and  prob- 
ably acuminate  at  apex.  The  margin  is  finely  serrate,  with  rather 
obtuse  teeth. 

This  species  is  closely  related  to,  if  not,  indeed,  identical  with,  Jug- 
lans  oregoniana  Lx. ,  from  the  Chalk  Bluffs  of  California.  Almost 
the  only  difference  is  that  J.  oregoniana  is  enlarged  upward,  whereas 
the  one  under  discussion  is  narrowed  above  and  enlarged  below.  The 
configuration  of  the  base,  the  serrate  margins,  and  the  nervation  are 
very  similar.  There  are,  however,  no  intermediate  secondaries  in  J. 
oregoniana.  On  account  of  these  differences,  slight  though  they  are, 
and  from  the  further  fact  that  the  material  is  very  scanty,  it  has  been 
thought  best  to  regard  them  as  distinct,  at  least  for  the  present. 

Locality :  Two  miles  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 


724  IDAHO    MINING    DISTRICTS. 

MYRICA  LANCEOLATA  n.  sp. 
PI.  XCIX,  figs.  5,  6. 

Leaf  of  firm  texture ;  linear-lanceolate,  tapering  below  into  a  long 
wedge-shaped  base  which  passes  into  a  thick  petiole  lcm  to  2cm  long; 
apex  broken  but  apparently  long  acuminate;  margin  irregular,  faintly 
toothed;  midrib  very  thick,  straight;  secondaries  obscurely  preserved, 
but  apparently  alternate,  at  an  acute  angle,  and  passing  up  for  long 
distances  near  the  margin ;  finer  nervation  hot  retained. 

This  species  is  based  on  the  two  fragments  figured,  both  of  which 
represent  the  basal  portion.  The  smaller  of  the  two  specimens  (fig.  6) 
is  6.5cm  in  length  including  the  petiole  (1CJU),  and  was  probably  at  least 
9. 5cm  in  length  when  perfect.  Its  width  is  abont .  75cm.  The  nervation, 
with  the  exception  Of  the  thick  midrib,  is  not  preserved.  The  larger 
leaf  has  only  5.5cm  preserved,  including  the  petiole  of  2cm.  Its  length 
must  have  been  at  least  12cm.  The  midrib  is  very  thick  and  straight, 
as  in  the  other.  The  width  of  this  specimen  is  a  little  more  than  1. 5cm. 

This  species  is  very  closely  allied  to  a  species  not  yet  published, 
from  the  Lamar  flora,  in  the  Yellowstone  National  Park.  The  leaves 
are  of  about  the  same  size,  the  main  point  of  difference  being  the 
more  pronounced  teeth  in  the  Lamar  species. 

Locality:  Cartwright  ranch,  on  Shafer  Creek,  Boise  County,  Idaho. 

MYRICA  ?  IDAHOENSIS  n.  sp. 
PI.  XCIX,  fig.  7. 

Leaf  thickish,  obovate-lanceolate,  obtuse  at  apex,  narrowed  below 
to  a  wedge-shaped  base  and  a  long,  thick  petiole;  margin  obscurely 
crenate ;  midrib  thick,  straight. 

This  leaf  is  preserved  entire,  and  is  9cm  in  length,  including  the 
petiole,  which  is  2cm.  In  outline  it  is  long,  obovate-lanceolate,  with 
obtuse  apex,  and  narrowed  from  above  the  middle  to  a  long,  wedge- 
shaped  base.  The  petiole  is  thick  and  much  curved  to  one  side.  The 
margin  is  rather  remotely  and  faintly  crenate,  the  teeth  short  and 
obtuse/  The  midrib  is  the  only  nervation  preserved.,  and  this  is  thick 
and  straight. 

In  absence  of  better  nervation  there  is  some  doubt  as  to  the  generic 
reference  of  this  leaf.  It  has  been  referred  to  Myrica  provisionally, 
until  better  material  can  be  obtained.  It  has  considerable  resem- 
blance to  the  living  M.  cerifera  L.  (common  wax-berry),  but  it  is  impos- 
sible to  carry  the  comparison  beyond  similarity  of  shape,  dentation, 
and  midrib. 

Locality:  Two  miles  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 


KNOWLTON.]  PLANTS    OF    THE    PAYETTE    FORMATION.  725 

POPULUS  LINDGRENI  n.  Sp. 
PL  C,  fig.  3. 

Leaf  of  firm  texture,  coriaceous,  nearly  circular  in  outline,  being 
only  a  trifle  broader  below  the  middle,  whence  it  is  rounded  to  a  trun- 
cate base,  and  above  to  a  very  obtuse  apex;  margin  somewhat  irreg- 
ularly but  finely  crenate-toothed,  the  teeth  obtuse;  petiole  over  2cm 
in  length,  very  large,  flattened;  palmately  five-nerved  or  ribbed  from 
the  top  of  the  petiole,  the  central  or  midrib  strongest,  very  thick, 
the  two  lateral  ribs  also  strong,  the  lowest  pair  being  the  slightest; 
the  central  or  midrib  with  two  pairs  of  subopposite  secondaries  high 
above  the  middle ;  the  large  lateral  pairs  of  ribs  each  with  about  six 
secondaries  on  the  outside,  emerging  at  a  very  low  angle  and  arch 
ing  near  the  margin ;  finer  nervation  obscure. 

The  fine  specimen  figured  is  the  only  one  obtained  of  this  charac- 
teristic species.  It  is  nearly  circular  in  outline,  being  5.25cm  in  length 
without  the  petiole,  and  nearly  5.5cm  in  width  at  the  broadest  portion, 
which  is  just  below  the  middle.  The  petiole  is  a  little  more  than  2cm 
in  length,  2mm  in  width  as  it  emerges  from  the  base  of  the  leaf,  and 
3.5mm  in  width  at  the  other  end.  It  appears  to  be  preserved  entire 
and  is  clearly  flattened. 

The  margin  of  the  leaf  is  closely  crenate-toothed,  the  teeth  being 
obtuse.  The  nervation  is  markedly  five-ribbed  from  near  the  top  of 
the  petiole,  the  three  central  ribs  being  by  far  the  stronger.  The 
lowest  lateral  ribs  or  nerves  are  small  and  soon  lost  in  the  blade  of 
the  leaf. 

Among  living  species  this  appears  to  approach  most  closely  to  P. 
balsamifera  candicans.  It  differs  in  being  much  more  obtuse,  in 
having  a  more  marked  crenate  border,  and  in  the  stronger  nervation. 
The  relationship  is,  however,  quite  marked,  the  two  leaves  being  of 
the  same  type,  but  with  strong  specific  differences. 

There  is  no  fossil  American  species  with  which  this  is  to  be  closely 
compared.  There  are  several  with  approximately  the  same  shape, 
yet  differing  clearly  in  serration,  nervation,  etc. 

I  take  pleasure  in  naming  it  after  Mr.  Waldemar  Lindgren,  of  the 
United  States  Geological  Survey. 

Locality:  Two  miles  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 

POPULUS  EOTREMULOIDES  n.  Sp. 
PI.  C,  figs.  1,  2;  CI,  figs.  1,  2. 

Leaves  membranaceous  yet  firm-textured,  broadly  ovate  in  outline, 
rounded  regularly  to  the  base  and  contracted  above  to  an  obtusely 
acuminate  apex;  margin  entire  for  lower  fourth  of  leaf,  remainder 
obscurely  crenate-toothed ;  petiole  very  long,  flattened;  midrib  rather 


726  IDAHO    MINING    DISTRICTS. 

strong;  secondaries  about  four  or  five  pairs,  the  lowest  pair  arising 
from  the  very  base  of  the  blade,  thin,  soon  lost  in  the  blade ;  second 
pair  very  strong,  arising  from  the  petiole  some  distance  above  the 
base  and  arching  up  for  two-thirds  the  length  of  the  leaf,  probably 
branched  outside;  the  other  secondaries,  probably  two  or  three  pairs, 
arising  some  distance  above,  strong,  alternate,  at  an  angle  of  45° ; 
finer  nervation  not  retained. 

This  well-marked  species  is  represented  by  the  four  specimens  fig- 
ured. The  larger  of  these  (fig.  2  of  PL  CI)  is  10.75cm  in  length  with- 
out the  petiole,  which  is  5.25cm  long.  The  margin  is  not  all  preserved, 
but  the  leaf  appears  to  have  been  about  7cm  in  width.  The  other 
nearly  perfect  leaf  (fig.  1)  is  a  little  less  than  10cm  in  length  -and  is 
6.5cm  in  width.  About  3.5cra  in  length  of  petiole  is  preserved,  but  it 
is  not  all  present. 

The  leaves  are  all  broadly  ovate,  with  rounded  bases  and  obtuse 
apices.  The  margin  is  crenate-toothed  from  above  the  base.  The 
petiole  is  very  long,  as  may  be  seen  from  the  figures,  and  is  obviously 
flattened.  The  nervation  is  not  well  preserved,  but  enough  can  be 
made  out  to  show  its  general  character.  The  strong  pair  of  second- 
aries arise  some  distance  above  the  base,  while  the  thin  basal  pair 
arise  near  the  top  of  the  petiole.  There  are  also  two  or  three  pairs  of 
secondaries  arising  from  the  midrib  some  distance  above  the  strong 
pair.  None  of  the  ultimate  nervation  is  retained. 

Among  living  species  the  relation  of  this  fossil  form  is  unquestion- 
ably with  P.  tremuloides  Michx.  In  the  herbarium  of  the  National 
Museum  there  is  a  specimen,  consisting  of  a  young  seedling  plant  of 
this  species,  collected  on  the  Aquarius  Plateau,  Utah,  at  an  altitude 
of  9,000  feet,  that  can  hardly  be  distinguished  from  the  fossil  leaves 
under  consideration.  The  size,  outline,  petiole,  and  nervation  are 
practically  identical.  The  only  difference,  and  this  is  of  minor  im- 
portance, appears  to  be  in  the  margin.  In  the  fossil  form  the  teeth 
are  absent  from  the  lower  fourth  of  the  leaf,  while  these  specimens 
of  P.  tremuloides  are  toothed  from  base  to  apex  and  the  teeth  are 
rather  larger.  The  leaves  of  this  seedling  differ  somewhat  from  the 
normal  mature  leaves  of  the  species,  but  it  would  seem,  in  view  of 
their  evident  relationship  to  the  fossil  leaves,  that  they  represent  a 
reversion  to  an  ancestral  type,  or  perhaps  rather  a  survival  of  this 
type,  which  disappears  in  the  mature  plant,  There  certainly  can  be 
no  doubt  of  the  intimate  relationship  between  the  living  and  fossil 
leaves. 

There  seems  to  be  no  fossil  American  species  with  which  it  is  at  all 
intimately  related.  It  is  perhaps  closest  to  P.  zaddachi  Heer,  but 
differs  markedly. 

I  have  given  this  species  the  name  eotremuloides  in  view  of  its 
evident  relation  to  the  well-known  tremuloides. 

.  Locality:  Two  miles  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 


KNOWLTON.]  PLANTS    OF   THE   PAYETTE    FORMATION.  727 

POPULUS   OCCIDENTALS  n.  Sp. 
PI.  XCIX,  fig.  14. 

Leaves  evidently  of  firm  texture,  long-ovate  in  outline,  rounded 
below  to  a  truncate  base  and  narrowed  above  (apex  broken) ;  petiole 
not  preserved;  margin  faintly  or  rather  obscurely  crenate-toothed, 
with  obtuse  teeth;  midrib  slender,  straight;  secondaries  seven  or 
eight  pair,  subopposite,  at  an  angle  of  about  45°,  curving  upward ; 
finer  nervation  not  preserved. 

This  species  is  represented  by  the  single  example  figured.  The 
part  preserved  is  8cm  long  and  was  probably  not  far  from  10cm  in  length 
when  perfect.  It  is  broadest  at  a  point  much  below  the  middle,  where 
it  is  6cm  broad.  Both  base  and  apex  are  wanting,  but  it  appears  that 
it  was  rounded  or  truncate  at  base  and  acuminate  at  apex.  The  mar- 
gin is  rather  obscurely  crenate-toothed,  the  teeth  obtuse.  The  nerva- 
tion consists  of  about  eight  pairs  of  subopposite  secondaries. 

This  species  seems  to  approach  quite  closely  to  Populus  monilifera 
Ait. ,  the  cottonwood  so  abundant  in  the  West.  It  differs  slightly  in 
dentation  of  the  margin,  and  in  the  fact  that  the  secondaries  arise  at 
a  greater  angle  and  apparently  do  not  anastomose  near  the  margin. 

Among  fossil  species  it  is  somewhat  related  to  P.  balsamoides  Gopp. , 
from  the  Miocene  of  California.1  But  this  differs  in  being  more  heart- 
shaped  at  base,  more  obtuse  at  apex,  and  more  strongly  dentate  at 
margin. 

Locality:  Two  miles  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 

SALIX  ANGUSTA  Al.  Br. 

PL  XCIX,  fig.  12. 

There  are  a  number  of  somewhat  defective  leaves  that  are  referred 
with  little  doubt  to  this  species. 

Localities:  One  mile  southeast  of  Marsh  post-office,  Boise  County; 
Cartwright's  ranch,  on  Shafer  Creek,  Idaho. 

BETULA  ANGUSTIFOLIA  Newby. 
Proc.  U.  S.  Nat.  Mus.,  Vol.  V,  p.  508,  1883;  plates  ined.,  PI.  XL VI,  fig.  5. 

This  was  described  by  Newberry  from  Bridge  Creek,  Oregon.  The 
specimen  here  referred  to  it  is  broken,  but  is  probably  correctly 
identified. 

Locality:  Idaho  City,  Idaho. 

BETULA,  Fruit  of. 
PI.  XCIX,  fig.  9. 

Fruit  (pistillate  ament)  cylindrical,  3cm  in  length,  9mm  in  diameter; 
bracts  rather  few,  acutish,  about  3mm  long. 

1  Lx.,  Cret.  and  Tert.  Fl.,  p.  348,  PL  LV,  figs.  3,  5, 1883. 


728  IDAHO    MINING    DISTRICTS. 

This  appears  to  represent  the  pistillate  ament  of  a  Betula,  agreeing, 
for  example,  quite  closely  with  the  living  B.  alba,  B.  papyracea,  etc. 
This  view  is  further  strengthened  by  the  finding  of  leaves  of  Betula 
in  the  same  beds. 

I  have  not  thought  best  to  name  it  specifically,  as  it  is  somewhat 
obscure  and  better  material  is  necessary  for  the  determination  of  the 
minute  characters. 

Locality:  Two  miles  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 


BETULA  ^QTJALIS?  Lx. 

PL  Oil,  fig.  5. 

Betula  cequalis  Lx.,  Mem.  Mus.  Comp.  Zool.,  Vol.  VI,  No.  1,  p.  2,  PI.  I,  figs. 
2-4,  1880. 

I  am  somewhat  in  doubt  as  to  the  correctness  of  this  reference. 
There  is  but  a  single  specimen  in  the  collection,  and  this,  as  may  be 
seen  from  the  figure,  is  not  perfect,  lacking  the  apex  and  most  of  one 
side  and  the  base.  It,  however,  agrees  quite  closely  with  Lesquereux's 
figures,  being  only  a  little  more  obtuse.  The  base  appears  similar  as 
far  as  can  be  made  out. 

Locality:  Two  miles  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 

QUERCUS   SIMULATA  n.  8p. 
PL  CI,  figs.  3,  4;  Oil,  figs.  1,  2. 

Leaves  coriaceous,  lanceolate-acuminate,  slightly  unequal  sided  at 
base,  obtuse  or  obtusely  acuminate  at  apex;  margin  undulate  or 
remotely  shallow-toothed;  petiolate,  petiole  short,  thick;  midrib 
strong,  straight;  secondaries  numerous,  12  to  16  pairs,  alternate  or 
subopposite,  at  an  angle  of  20°  to  45°,  irregular,  camptodrome,  each 
joined  by  a  simple  bow  to  the  one  next  above;  intermediate  second- 
aries occasional,  soon  vanishing;  ultimate  nervation  obscure,  but 
apparently  quadrangular. 

These  leaves  appear  to  have  been  quite  abundant  in  the  beds,  for 
four  or  five  very  perfect  examples,  and  numerous  more  or  less  frag- 
mentary ones,  occur  in  the  collection.  They  were  evidently  thick, 
coriaceous  leaves,  suggestive  at  least  of  having  been  evergreen.  They 
range  considerably  in  size,  the  smallest  being  3cm  in  length  and  lcm  in 
width,  and  the  largest  9cm  in  length  and  2.25cm  in  width.  The  average 
size,  represented  by  figs.  1  and  4,  is  about  8cm  in  length  by  2cm  in 
width.  In  the  smaller  specimens  the  petiole  is  scarcely  2m™  long, 
while  in  the  larger  ones  it  is  nearly  or  quite  lcm  in  length.  They  are 
slightly  unequal-sided  at  base,  and  obtuse  (fig.  1)  or  somewhat  acumi- 
nate (fig.  4)  at  apex.  The  margin  is  undulate,  or  very  slightly  and 
remotely  toothed. 


KNOWLTON.]  PLANTS    OF    THE    PAYETTE    FORMATION.  729 

The  nervation  is  marked  at  once  by  the  great  number  of  close  camp- 
todrome  secondaries  that  arise  at  various  angles  from  perhaps  20°  to 
45°.  The  finer  nervation  is  obscure. 

Among  living  species  this  appears  to  approach  most  closely  to 
Q.  imbricaria  MX.,  which  has  the  same  shape,  the  inequilateral  base, 
and  the  undulate  margin.  The  differences  in  the  primary  nervation 
are,  however,  marked.  In  Q.  imbricaria  the  secondaries  are  not 
nearly  so  numerous ;  they  emerge  at  a  more  acute  angle  and  are  more 
irregular  in  their  course.  They  are  camptrodrome,  somewhat  as  in 
Q.  simulata. 

Among  fossil  species  the  one  under  discussion  approaches  Q.  sim- 
plex Newby.,  from  Bridge  Creek,  Oregon,1  which  differs  in  being  nar- 
rower, with  more  acuminate  apex,  and  in  having  fewer  secondaries. 
Ours  is  also  somewhat  like  Q.  convexa  Lx. ,  of  the  auriferous  gravels 
of  California,  which  differs,  however,  in  being  rather  oblanceolate 
with  more  obtuse  apex.  The  nervation  is  of  the  same  character  in 
both,  and  they  are  evidently  related. 

Locality:  Two  miles  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 

QUERCUS  CONSIMLLIS  Newby. 

PI.  Oil,  fig.  6. 

Quercus  consimilis  Newby.,  Proc.  TJ.  S.  Nat.  Mus.,  Vol.  V,  p.  505,  1883;  plates 

ined.,  PI.  LXIII,  figs.  2-5. 
Quercus  breweri  Lx.,  Cret.  and  Tert.  Fl.,  p.  246,  PI.  LIV,  figs.  5-8,  1883. 

This  species  is  represented  by  the  very  perfect  figured  specimen 
and  also  a  number  of  equally  well  preserved  but  broken  specimens. 
There  can  be  no  doubt  as  to  its  belonging  to  Newberry's  species, 
which  is  from  Bridge  Creek,  Oregon. 

Localities:  Two  miles  southeast  of  Marsh  post-office;  1  mile  south- 
east of  Marsh  post-office,  Boise  County,  Idaho. 

QUERCUS  IDAHOENSIS  n.  sp. 
PL  Oil,  fig.  4. 

Leaves  coriaceous,  broadly  oblong  in  general  outline,  rather  abruptly 
rounded  at  base,  obtusely  acuminate  at  apex,  margin  sharply  serrate 
to  just  below  the  apex;  the  teeth  large,  almost  bristle-pointed,  directed 
upward,  sinuses  deep,  rounded;  midrib  rather  thin,  straight;  second- 
aries about  10  or  12  pairs,  straight,  parallel,  craspedodrome,  entering 
the  larger  teeth,  arising  at  an  angle  of  about  45°,  subopposite;  finer 
nervation  not  preserved. 

This  species  is  represented  by  the  single  example  figured.  It  is  8cm 
long  and  3cm  wide.  It  lacks  only  a  very  small  portion  of  the  base.  It 

» Proc.  U.  S.  Nat.  Mus.,  Vol.  V,  p.  505, 1883;  Plates  ined.,  PI.  XLIII,  flg.  6. 


730  IDAHO    MINING   DISTRICTS. 

is  quite  a  striking  leaf,  being  made  so  by  the  regular,  sharp-pointed 
teeth  and  the  parallel  craspedodrome  secondaries. 

This  species  is  closely  allied  to  the  preceding  species,  Q.  consimilis, 
and  it  is  possible  that  it  may  belong  to  it.  It  appears  to  differ  in  its 
larger  size,  larger  and  stronger  teeth,  and  particularly  in  being  toothed 
entirely  to  the  base,  whereas  Q.  consimilis  is  without  teeth  for  nearly 
or  quite  one-third  of  its  length.  A  larger  series  may  show  them  to 
be  identical. 

Locality:  Two  miles  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 

QUERCUS  SIMPLEX  Newby. 
Proc,  U.  S.  Nat.  Mus.,  Vol.  V,  p.  505,  1883;  plates  ined.,  PI.  XLIII,  fig.  6. 

There  are  two  or  more  fairly  well  preserved  examples  that  appear 
to  belong  to  this  species. 

Locality:  One  mile  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 

QUERCUS  PAYETTENSIS  n.  sp. 

PL  CII,  fig.  9. 

Leaves  of  firm  texture,  lanceolate  in  outline ;  margin  deeply  sinuate- 
toothed,  the  teeth  rather  obtuse,  the  sinuses  deep,  rounded;  midrib 
strong;  nervation  craspedodrome;  secondaries  as  many  pairs  as  there 
are  teeth,  alternate,  at  an  angle  of  about  45°,  passing  straight  to  and 
entering  the  teeth ;  finer  nervation  not  retained. 

This  species  is  founded  on  the  example  figured  and  one  or  two  addi- 
tional fragments.  The  figured  specimen  is  the  most  perfect,  though 
lacking  both  base  and  apex.  It  is  now  about  4.5cm  in  length  and 
1.75cm  in  width.  It  was  probably  not  far  from  7cm  in  length  when 
perfect. 

This  species  has  comparatively  little  resemblance  to  either  of  the 
species  of  Quercus  detected  thus  far  in  the  Payette  formation.  It  is 
perhaps  closest  to  Q.  consimilis  Newb.  (PI.  IV,  fig.  6),  but  differs 
markedly  in  being  longer,  narrower,  and  in  having  much  stronger 
teeth.  Quercus  furcinervis  Rossm.,1  from  Bridge  Creek,  Oregon,  is 
somewhat  similar,  being,  however,  very  much  larger  and  with  rela- 
tively much  smaller  teeth. 

Locality:  Silicified  shale,  Jackass  Creek,  1£  miles  above  its  junction 
with  the  Payette  River,  Boise  County,  Idaho. 

QUERCUS  ?  sp. 

There  is  a  single  fragment  that  appears  to  belong  to  this  genus,  but 
it  is  too  much  broken  to  permit  identification.  It  is  a  leaf  that  must 
have  been  12cm  or  14cm  in  length  and  about  5cm  in  width.  The  basal 

i  Lx.,  Cret.  &  Tert.  PI.,  PI.  LIV,  fig  2. 


KNOWLTON.]  PLANTS    OF    THE    PAYETTE    FORMATION.  731 

portion  only  is  preserved.  The  leaf  appears  to  have  been  obovate- 
lanceolate,  extending  below  into  a  wedge-shaped  base.  It  appears  to 
have  been  entire  in  the  lower  portion  and  toothed  above. 

Locality:  One  mile  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 

ULMUS  SPECIOSA  Newby. 

Proc.  U.  S.  Nat.  Mus.,  Vol.  V,  p.  507,  1883;  Plates  ined.,  PI.  XLV,  fig.  8. 

A  single,  somewhat  fragmentary  specimen,  but  with  no  doubt  this 
species. 

Locality:  Idaho  City,  Idaho. 

FlCUS   UNGERI   Lx. 
Pi   CI,  fig.  5. 

Lesquereux,  Suppl.  to  Hayden's  Ann.  Rept.  1871,  p.  7  (1872);  Tert.  Fl.,  p.  195,  PI. 
XXX,  fig.  3;  Cret.  &  Tert.  Fl.,  p.  163,  PI.  XLIV,  figs.  1-3. 

The  collection  contains  three  specimens  that  undoubtedly  belong 
to  this  species,  being  especially  like  fig.  2  of  PL  XLIV  in  the  Cretaceous 
and  Tertiary  Flora.  They  are  of  about  the  size  of  this,  and  have  the 
slightly  unequal  base  and  identical  nervation. 

Locality:  Cartwright's  ranch,  on  Shafer  Creek,  Boise  County,  Idaho. 

CASSIA  OBTUSA  n.  sp. 
PL  C,  figs.  4,  5. 

Leaflet  small,  of  firm  texture,  elliptical;  margin  entire,  obtuse  at 
apex,  obtuse  or  subcordate  at  base;  petiole  short,  thick;  midrib 
thick,  straight ;  secondaries  numerous,  about  14  pairs,  the  lowest  pair 
short,  nearly  at  right  angles  to  the  midrib,  the  others  alternate,  at  an 
angle  of  20°  to  30°,  probably  curving  and  anastomosing  at  their 
extremities;  finer  nervation  not  preserved. 

The  two  examples  figured  are  all  of  this  species  that  were  contained 
in  the  collection.  The  smaller  is  about  3.5cm  in  length  and  1.5cm  in 
width.  It  is  nearly  regularly  elliptical  in  outline,  with  obtuse  base 
and  relatively  obtuse  apex.  The  petiole  is  a  little  more  than  lmm  in 
length  and  is  rather  thick.  The  midrib  is  also  thick  and  carries 
about  fourteen  pairs  of  alternate  parallel  close  secondaries.  The 
other  specimen  is  a  little  longer,  with  a  subcordate  base,  but  is  other- 
wise similar. 

There  seems  to  be  no  American  ^species  with  which  this  can  be 
closely  compared,  but  in  the  Swiss  Tertiary  a  number  of  forms 
approach  it  quite  closely.  Thus  Cassia  phaseolites  Heer1  suggests 
this,  but  differs  in  size  and  in  the  fact  that  it  is  more  wedge-shaped 
at  base  and  apex.  The  nervation  is  quite  similar.  C.  ambigua  Heer  2 

i  Fl.  Tert.  Helv.,  Vol.  Ill,  PI.  CXXXVII,  figs.  1-13. 
"Loc.  cit.,  figs.  29,  32. 


732  IDAHO   MINING   DISTRICTS. 

is  also  similar,  but  differs  in  outline  and  in  having  fewer  secondaries. 
As  nearly  as  can  be  made  out,  the  leaflets  under  consideration  belong 
to  this  genus  and  are  provisionally  so  placed. 

Locality :  Two  miles  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 

PLATANUS  ASPERA  ?  Newb. 
Proc.  U.  S.  Nat.  Mus.,  Vol.  V,  p.  509,  1883;  Plates  ined.,  PI.  XLII,  figs.  1-3. 

The  collection  contains  several  fragments  of  Platan  us  leaves,  but 
hardly  enough  to  be  certain  of  their  reference  to  this  species.  It  is 
probable,  however,  that  the  identification  is  correct. 

Locality:  One  mile  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 

CELASTRUS  LINDGRENI  n.  sp. 
PL  XCIX,  fig.  13;  C,  fig.  6. 

Leaf  membranaceous ;  lanceolate-oblong  in  outline,  narrowed  below 
into  a  wedge-shaped  base  and  prolonged  above  into  an  acuminate 
apex;  margin  obscurely  serrate,  the  teeth  small,  obtuse;  midrib 
rather  thick  and  strong;  secondaries  about  10  or  12  pairs,  suboppo- 
site,  emerging  at  an  angle  of  45°  or  more,  camptodrome,  each  arched 
and  joined  to  the  one  above  by  a  broad  loop  some  distance  within  the 
border,  with  one  series  of  smaller  loops  outside  from  which  weak 
branches  pass  to  the  teeth;  intermediate  secondaries  occasionally 
present,  soon  lost;  nervilles  much  broken,  forming  large,  irregular 
areolse. 

The  somewhat  fragmentary  leaves  figured  are  the  only  specimens  of 
this  form  in  the  collection.  The  smaller  appears  to  have  been  about 
6.5cm  in  length,  and  a  little  more  than  2cm  in  width  at  the  broadest 
point,  which  is  a  little  below  the  middle  of  the  leaf.  The  larger  leaf 
was  8  or  9cm  in  length,  and  is  about  3.8cm  in  width.  The  nervation  of 
both  is  finely  preserved,  and  is  quite  characteristic  of  the  genus 
Celastrus. 

The  species  with  which  this  is  to  be  compared  is  Celastrus  frax- 
inifolius  Lx./from  Florissant,  Colorado.  The  general  resemblance  is 
very  marked,  the  differences  being  rather  of  minor  or  specific  impor- 
tance. They  are  as  follows :  In  C.  fraxinifolius  the  leaves  are  broad- 
est below  the  middle,  the  petiole  is  winged  (broken  in  C.  lindgreni), 
the  teeth  are  fewer  and  stronger,  .and  the  secondaries  fewer. 

Among  the  numerous  new  species  of  this  genus  found  in  the  Yel- 
lowstone National  Park,  but  still  unpublished,  there  are  several  to 
which  this  is  evidently  related. 

Locality :  Idaho  City,  Idaho. 

'  Cret.  and  Tert.  Fl.,  p.  184,  PI.  XXXIII,  figs.  2-4;  XL,  fig.  10. 


KNOWLTON.]  PLANTS    OF   THE   PAYETTE   FORMATION.  733 

ACER  TRILOBATUM  PRODUCTUM  ?  Heer. 
PL  CII,  fig.  3. 

The  collection  contains  only  the  single  specimen  figured  of  this 
form.  It  is  unfortunately  broken  at  the  apex,  so  that  its  reference  to 
this  variety  of  Acer  trilobatum  is  more  or  less  uncertain.  From  the 
configuration  of  the  part  preserved  there  is,  however,  little  doubt  as 
to  its  correctness. 

Locality :  Two  miles  southeast  of  Marsh  post-office,  Boise  County* 
Idaho. 

RHUS  PAYETTENSIS  n.  sp. 

PI.  CI,  figs.  6,  7. 

Leaflet  coriaceous,  ovate  in  outline,  abruptly  rounded  or  truncate 
at  base,  and  slightly  unequal-sided,  obtuse  (?)  at  apex;  margin  nearly 
entire  on  one  side,  remotely  toothed  on  the  other,  the  teeth  small, 
sharp,  pointing  upward;  midrib  thin,  somewhat  irregular;  seconda- 
ries about  6  or  7  pairs,  opposite  or  subopposite,  emerging  at  an  angle 
of  35°,  much  curved  upward,  and  ending  in  or  sending  weak  branches 
to  the  few  marginal  teeth;  nervilles  strong,  mainly  percurrent;  finer 
nervation  quadrangular. 

The  smallest  leaflet  is  5.25cm  in  length  as  now  preserved,  and  was 
probably  not  far  from  6cm  in  length  when  perfect.  It  is  just  3cm  in 
width.  The  whole  base  is  unfortunately  not  preserved^  but  from  the 
configuration  it  appears  that  it  was  slightly  unequal-sided. 

This  species  is  referred  to  the  genus  Rhus  on  the  strength  of  its 
resemblance  to  the  living  Rhus  toxicodendron,  the  common  poison  ivy. 
This  small  leaflet  resembles  certain  small  forms  of  this  species  in 
quite  a  marked  degree.  The  living  form  has  usually  more  strongly-cut 
leaflets,  but  in  general  outline  and  nervation  they  are  quite  similar. 

This  species  does  not  appear  to  be  particularly  close  to  any  of  the 
numerous  fossil  species  that  have  been  described  from  similar  beds. 

Locality:  Two  miles  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 

TRAPA  AMERICANA  n.  sp. 
PL  CII,  fig.  7a. 

Fruit  two-horned,  the  horns  long,  slender,  acuminate,  pointing 
upward  at  an  angle  of  about  45° ;  central  prominence  between  the 
horns  obtuse,  prominently  striate ;  body  of  fruit  thick,  wedge-shaped 
below. 

This  fruit  belongs  to  the  two-horned  Asiatic  type  of  the  genus.  It 
is  obverse-deltoid  or  broadly  wedge-shaped  in  outline.  The  distance 
from  base  to  extremity  of  horn  is  just  2cm,  while  the  distance  between 


734  IDAHO    MINING  DISTRICTS. 

the  horns  is  about  17mm.  The  length  from  base  to  tip  of  central  promi- 
nence is  16mm.  The  length  of  the  horns  is  about  7mm,  and  the  length 
of  the  central  prominence  about  4mm. 

Thus  far  only  two  specimens  of  Trapa  have  been  described  from 
North  America — T.  borealis  Heer,1  from  the  Eocene  of  Port  Graham, 
Alaska,  also  detected  by  Dawson  in  the  Laramie  of  Red  Deer  and 
Rosebud  rivers,  Canada,  and  Trapa  (?)  microphylla  Lx.,2  described 
from  Point  of  Rocks,  Wyoming,  and  since  detected  near  the  mouth 
of  the  Yellowstone  River  in  Montana,  in  the  Yellowstone  National 
Park,  in  the  Ceratops  beds  of  "Wyoming,  and  along  the  Red  Deer  and 
Rosebud  rivers  in  Canada.  Some  doubt  attaches  to  the  correctness 
of  the  reference  of  the  last  to  Trapa,  as  the  specimens  are  leaves  or 
leaflets  only;  but  as  they  have  been  found  by  Dawson  associated  with 
fruit,  it  may  be  correct. 

The  ordinary  form  of  T.  borealis,  as  described  and  figured  by  Heer 
(loc.  cit.),  is  quite  different  from  the  one  in  hand,  being  very  thick 
and  obtuse  at  base,  with  irregular  horns  and  a  greatly  enlarged  cen- 
tral projection.  One  of  Heer's  figures  (op.  cit.,  fig.  11),  however,  is 
quite  like  ours  in  shape,  but  is  more  than  twice  the  size. 

The  species  from  Idaho  is  perhaps  more  like  T.  silesiaca  Gopp., 
described  from  Schossnitz,  Silesia,  and  also  detected  by  Heer  in  Por- 
tugal.3 It  is  about  the  same  size,  but  differs  slightly  in  the  slenderer 
horns  and  entire  central  prominence. 

Locality:  Idaho  City,  Idaho. 

TRAPA  ?  OCCIDENTALIS  n.  sp. 
PL  Oil,  fig.  7b. 

Fruits  two-horned,  or  in  effect  three-horned,  the  lateral  horns  slen- 
der, acute,  at  right  angles  to  the  central  prominence  or  horn,  which 
is  nearly  twice  the  size  of  the  lateral  ones;  body  of  the  fruit  but  little 
prolonged  below  the  plane  of  the  lateral  horns,  slightly  wedge-shaped.  • 

These  fruits  are  decidedly  anomalous.  They  are  deltoid  or  trian- 
gular in  general  outline.  The  width  is  2cm,  each  lateral  horn  being 
5  or  6mm  in  length  and  2mm  in  width  at  the  base.  -  The  central  pro- 
jection is  1.5cm  in  length  and  about  5mm  in  width  at  the  base. 

I  am  much  in  doubt  as  to  whether  these  fruits  should  be  referred 
to  the  genus  Trapa.  They  are  found  in  the  same  piece  of  matrix  as 
the  one  previously  characterized,  and  in  fact,  as  may  be  seen  from 
the  figure,  one  of  them  overlaps  one  of  the  horns  of  T.  americana. 
Close  association  of  unconnected  fossils  does  not,  of  course,  argue 
affinity,  but  these  are  so  close  together  and  have  such  a  general 

1  PI.  Poss.,  Alaska,  p.  38,  PI.  VIII,  figs.  9-14 

5  Bull.  U.  S.  Geol.  and  Geogr.  Surv.  Terr.,  Vol.  I,  p.  369,  1875;  Tert.  PI.,  p.  295,  Pl.'LXI,  figs. 
16-lTa;  Ward,  Bull.  U.  S.  Geol.  Surv.  No.  37,  p.  64,  PI.  XXVII,  figs.  3-5, 1887. 
3  Contr.  PI.  Poss.  Portugal,  p.  37,  PI.  XXII,  fig.  11, 1881. 


KNOWLTON.]  PLANTS    OP    THE    PAYETTE    FORMATION.  735 

resemblance  that  it  has  been  thought  best  to  describe  them  under 
this  name.     A  more  obvious  affinity  will  be  accepted  if  pointed  out. 
For  geological  purposes  this  species  will  serve  admirably. 
Locality:  Idaho  City,  Idaho. 


PHYLLITES  FLEXUOSUS  n.  sp. 
PL  Oil,  fig.  8. 

Leaf  membranaceous,  outline  probably  broadly  lanceolate;  base 
and  apex  destroyed ;  margin  undulate-toothed ;  midrib  strong,  straight ; 
secondaries  many  pairs,  alternate,  straight  or  oftener  very  flexuose, 
camptodrome  or  subcraspedodrome,  entering  the  obscure  blunt  teeth; 
finer  nervation  not  retained. 

This  is  only  a  fragment,  and  perhaps  should  not  be  given  a  name, 
but  it  appears  to  be  quite  characteristic,  and  hence  has  been  given 
this  preliminary  name  pending  the  discovery  of  more  perfect  material. 
The  width  is  about  6.5cni. 

No  attempt  has  been  made  to  search  for  affinities,  as  it  is  too  frag- 
mentary to  afford  satisfactory  diagnostic  characters  for  comparison. 

Locality:  Two  miles  southeast  of  Marsh  post-office,  Boise  County, 
Idaho. 

PHYLLITES  OBSCURUS  n.  sp. 
PI.  XCIX,  figs.  10,  11. 

Leaves  small,  elongated-elliptical,  with  entire  margins;  petiole 
long,  thick;  midrib  thick,  straight;  other  nervation  not  preserved. 

The  two  little  leaves  figured  are  all  that  were  contained  in  the 
present  collection.  The  smaller  is  2cm  in  length,  and  about  6mm  wide. 
The  petiole  is  about  4mm  in  length.  The  larger  leaf  was  about  3.5om 
in  length  and  about  8mm  in  width.  The  petiole  is  about  8mm  in 
length. 

As  the  nervation  is  not  preserved,  it  is  impossible  to  refer  these 
leaves  to  a  known  genus  with  any  degree  of  certainty.  They  are 
consequently  not  of  great  importance. 

Locality:  Two  miles  southeast  of  Marsh  post-office,  Boise  County, 
Idaho.  ' 

DISCUSSION  OF    THE    FLORA    AND    ITS  BEARING  ON  THE 
AGE  OF  THE  BEDS. 

As  here  enumerated,  the  flora  of  the  Payette  formation  embraces  32 
forms.  Of  this  number,  17  are  described  as  new,  while  5  are  not  spe- 
cifically named,  thus  leaving  only  10  species,  or  nearly  33  per  cent, 


736 


IDAHO    MINING   DISTRICTS. 


having  an  outside  distribution.     The  following  table  shows  graphically 
the  distribution  of  these  species : 

Distribution  of  the  flora  of  the  Payette  formation. 


Carbon,  Wyoming. 

Sedalia,  Colorado. 

* 

st 

2a 

a 

B 

£ 
a 

Auriferous  gravels, 
California. 

1 
1- 

t*  o 

O  to 
f 

M 
I 

m 

£ 

• 

1 

>a 
Kfi 

&& 
1 

•-a 

Sequoia  angustifolia  Lx  

x 

x 

Salix  angusta  ?  Al.  Br  

x 

x 

Betula  angustifolia  Newb  - 

x 

Betula  aequalis  Lx  

x 

Quercus  simplex  Newb  ... 

x 

Quercus  consimilis  Newb  

x 

x 

Ulmus  speciosa  Newb  

x 

Ficus  ungeri  Lx.  

x 

Platanus  aspera  Newb  

x 

Acer  trilobatum  productum  ?  Heer 

x 

x 

X? 

From  this  table  it  appears  that  9  of  the  10  species  are  found  in  the 
lone  formation  (auriferous  gravels)  of  California,  or  the  Miocene  of 
Bridge  Creek  and  the  John  Day  Valley,  Oregon,  and  that  6  of  the 
species  have  never  before  been  found  outside  of  these  places.  Of  the 
3  species  also  reported  from  the  Green  River  group,  Sequoia  angusti- 
folia, as  reported  from  California,  is  probably  not  the  same  as  the 
original  from  Nevada,  as  stated  in  the  systematic  portion.  Salix 
angusta  is  open  to  more  or  less  question,  being  difficult  of  positive 
identification  at  all  times.  The  remaining  species,  Ficus  ungeri, 
appears  to  be  found  in  the  Green  River  group  and  the  Payette.  Acer 
trilobatum  productum  is  doubtfully  identified  from  the  collection 
under  discussion,  and  is  therefore  entitled  to  but  little  consideration. 

Several  of  the  species  here  described  as  new  to  science  are  related, 
in  some  cases  closely,  to  certain  Miocene  species.  Thus,  Quercus  ida- 
hoensis  is  close  to  Q.  consimilis  Newb. ;  Populus  occidentalis  is  related 
to  P.  balsamoides  Gopp. ;  Quercus  simulata  is  somewhat  like  Q.  sim- 
plex Newb. ;  Myrica  lanceolata  and  Celastrus  lindgreni  are  clearly 
related  to  species  not  yet  published  from  the  Lamar  flora  of  the  Yel- 
lowstone National  Park. 

The  evidence  of  the  fossil  plants  points,  therefore,  to  the  Upper 
Miocene  age  of  the  Payette  formation,  a  view  which  is  confirmed  by 
the  stratigraphy.  In  fact,  the  close  relation  brought  out  between  this 
flora  and  that  of  Bridge  Creek  and  John  Day  Valley  and  the  fact 
that  the  western  limit  of  these  beds  as  now  explored  is  in  the  direc- 
tion of  these  localities  make  it  more  than  possible  that  they  may  be 
parts  of  a  formation  of  wide  extent. 


PLATE  XCIX. 


18  GEOL,  PT  3 47  737 


PLATE  XCIX. 

Page 

FIG.  1.  Dryopteris  idahoensis  n.  sp 721 

FIG.  2.  Dryopteris  idahoensis.     Fragment 721 

FIG.  3.  Pinus  sp._ 722 

FIG.  4.  Sequoia  angnstif olia  Lx 722 

FIGS.  5,  6.  Myrica  lanceolata  n.  sp  _ . . 724 

FIG.  7.  Myrica  idahoensis  n.  sp 724 

FIG.  8.  Juglans  hesperia  n.  sp 723 

FIG.  9.  Betula,  fruit  of 727 

FIGS.  10, 11.  Phyllites  obscurus  n.  sp 735 

FIG.  12.  Salix  angusta?  Al.  Br 727 

FIG.  13.  Celastrus  lindgreni  n.sp 732 

FIG.  14.  Populus  occidentalis  n.  sp._ 727 

738 


U.    S.    GEOLOGICAL  SURVEY 


EIGHTEENTH  ANNUAL  REPORT      PART  III      PL.    XCIX 


13 


FOSSIL  PLANTS  OF  THE  PAYETTE  FORMATION. 


PLATE  C. 


739 


PLATE  C. 

Page. 

PIGS.  1, 2.  Populus  eotremuloides  n.  sp 725 

Fio.  3.  Populus  lindgreni  n.  sp 725 

FIGS.  4,  5.  Cassia  obtusa  n.  sp 731 

FIG.  6.  Celastrus  lindgreni  n.  sp 732 

740 


U.    8.   GEOLOGICAL  SURVEY 


EIGHTEENTH  ANNUAL  REPORT      PART  III      PL.   C 


FOSSIL  PLANTS  OF  THE  PAYETTE  FORMATION. 


PLATE  CI. 


741 


PLATE  CI. 

Page. 

FIGS.  1,  2.  Populus  eotremuloides  n.  sp -..  725 

FIGS.  3,  4.  Quercus  simulata  n.  sp 728 

FIG.  5.  Ficusungeri  Lx 731 

FIGS.  6,  7.  Rhus  payettensis  n.  sp 733 

742 


U.   S.    GEOLOGICAL  SURVEY 


EIGHTEENTH  ANNUAL  REPORT      PART  III      PL.    Cl 


FOSSIL  PLANTS  OF  THE  PAYETTE  FORMATION. 


PLATE  On. 


743 


PLATE    OIL 

Page. 

FIGS.  1,2.  Quercus  simulata  n.  sp 728 

FIG.  3.  Acer  trilobatum  productum  ?  Heer 733 

FIG.  4.  Quercus  idahoensis  n.  sp 729 

FIG.  5.  Betulasequalis?  Lx 728 

FIG.  6.  Quercus  consimilis  Newby 729 

FIG.  7a.  Trapa  americana  n.  sp 733 

FIG.  7b.  Trapa?  occidentals  n.  sp 734 

FIG.  8.  Phyllites  flexuosus  n.  sp 735 

FIG.  9.  Quercus  payettensis  n.  sp 730 

744 


